Canon Update
After dealing with Castiel becoming a God-like form, and dying shortly after, Dean had been coming to terms with the death of his friend and the deteriorating mental state of his little brother, whose head was full of hallucinations of Lucifer and being inside The Cage in Hell. From the beginning of season 7 onwards, Dean becomes increasingly more depressed and turns more and more heavily towards drinking to solve his problems. Growing to be more jaded and bitter, Dean finds himself turning towards more black and white ways of dealing with hunting, especially shown when dealing with the Kitsune, Amy Pond. She had been killing criminals to take their pituitary glands to feed her dying son, and yet despite being asked specifically by Sam to leave her alive, instead Dean seeks her out behind Sam's back to kill her, but he leaves her son alive as he hasn't killed anyone. In general, Dean's attitude to monsters, through season 7, leads him to a simple mindset that either they're good or bad, and they only ever meet the bad ones, so they kill anything in their way. He is, however, faced with the reality of his own depression and self-loathing very early in the season when he is put on Supernatural Trial to defend his life against Osiris. Failing the trial (in which he must prove he does not hold any guilt), Dean is left to the hands of the ghost of Jo Harvelle, but Sam is able to rescue him by getting rid of Osiris. Despite this fact, Dean is left with the revelation that he isn't at fault for Jo and Ellen's deaths, but also that he'll never discover what's left of "Dean" until he lets go of a lot of the emotional baggage weighing him down.
Throughout season 7, the main antagonist is a monster known as the Leviathan. It is a biblical creature older than all creation. Leviathans are able to change into anyone once they've been touched by them and usually prefer to eat the original person to spare themselves any problems. The leader of these beings takes the role of a high class business man known as Richard "Dick" Roman, founder and CEO of Richard Roman Enterprises. Throughout the season, Dick is the source of constant problems (and a flurry of dick jokes) for the Winchesters, going so far as having two of his underlings masquerade as Sam and Dean and go on a killing spree in order of hunts that the boys did together since Sam left Stanford (meaning they started in the location in S1Ep1 and went onwards for several locations). Because of this, Sam and Dean were forced to deal with their dopplegangers and then had to hide the Impala and take on the fake names Tom (Dean) and John (Sam) Smith.
After dealing with their doubles, Sam discovered Dean had killed Amy. This set a strain on their relationship in which things between them become distant for a time, so much so that they go their separate ways, only to end up working the same case and getting roped into the situation together. It's here where Dean is contacted by Ellen Harvelle through a spiritual medium who tells him, again, to let go of his grief and guilt or it will kill him. Dean then apologises to Sam for betraying him and they hit the road together.
Shortly after that, Dean is faced with the distinct possibility of Sam leaving him for a normal married life. Despite the fact that Sam is drugged with a love potion and forcibly married (during their annual "Vegas Week", no less), he tries to be supportive until it comes to light that the whole thing is a sham. Still, this shows Dean is not prepared for the possibility of Sam leaving him behind, even if it means Sam will have a happy life with a woman he may love.
Following the wedding fiasco, and Sam's sham marriage being annulled, the two of them and Bobby get back to work on finding out what is happening at RRE. During this, Bobby is captured and the boys attempt to rescue him. As they are escaping, Bobby is shot in the head. Faced with the reality of their father-figure dying, both Sam and Dean handle it very differently. While Sam copes by making sure everyone who needs to know gets to know, Dean throws himself heavily into his work, trying to find out what is happening at RRE. It is during this time that the man who helped them cover their identities, Frank Devereaux, tells Dean that he can't keep running himself into the ground, and challenges him on the fact. The confrontation goes as follows:
Dean: I'm not going to quit. It's not even an option. I am not going to walk out on my brother.
Frank: Okay then fine. Do what I did.
Dean: What - go native? Stock up on C-rations?
Frank: No cupcake. What I did when I was 26 and came home to find my wife and two kids gutted on the floor. Decide to be fine 'til the end of the week. Make yourself smile because you're alive and that's your job. And do it again the next week.
Dean: So fake it?
Frank: I call it being professional. Do it right. With a smile. or don't do it.
Dean takes this advice to heart and, indeed, tries to do it right and be a professional. He is given a little time out (quite literally), when he's sent to 1944 to work a case with Eliot Ness concerning a time travelling god. It gives Dean some fun to be had in a bad time, perking him up quite a bit. The lifted mood helps Dean to get back into the swing of sleeping around but the woman he chooses (or is chosen by) for his first one night stand in years turns out to be an Amazon who uses Dean to give birth to an Amazon child, named Emma. Emma grows up in a matter of days to puberty at which point she is charged with killing her father to become a full-fledged warrior. Faced with his daughter, Dean tries to convince her to leave the Amazons and insists she hasn't killed yet and she doesn't need to. Instead, Emma tries to kill him and it is Sam who shoots her to protect Dean, putting both Sam and Dean on truly equal footing concerning Amy. Learning he had fathered a daughter and seeing Sam kill her took a lot out of Dean but he managed to bury the problem and move on, enjoying their next case (at Plucky Pennywhistle's Magical Menagerie where Sam is faced with his phobia of clowns and Dean gets both the chance to see his little brother covered in glitter and a giant rainbow slinky, thank you very much).
As their cases go on, Sam starts to succumb to his Lucifer hallucinations and Dean does what he can to help but it's a losing battle. Eventually Sam is checked into a hospital and Dean starts to look for a healer who might be able to fix Sam. It leads him into the path of a man named Emmanuel. It turns out that Emmanuel is actually Castiel without his memories, now married to a woman named Daphne who rescued him when she found him by a river without his memories. Emmanuel willingly comes with Dean to hopefully fix Sam. Shaken by the whole ordeal and still furious with Castiel for hurting Sam, Dean asks Emmanuel if he could actually be a bad person and simply not remember it, but Emmanuel says he does not feel like a bad person. Dean then explains that he is not able to forgive his friend Cas who betrayed him and caused Sam's illness. At the hospital, after meeting up with an old demon acquaintance named Meg, Emmanuel is forced to remember that he is Castiel in order for them to be able to get into the hospital and soon enough Castiel gets them in past the demons surrounding it, then taking on Sam's illness and remaining behind, insane and guarded by Meg, while Sam hits the road with Dean again.
Throughout the whole ordeal, Dean is emotionally weakened by seeing Castiel again and not really being able to take out his anger towards him. Having seen signs of things being moved around and having dealt with a haunting at a brewery, it is revealed that Bobby's spirit has been hanging around, attached to the flask that Dean carries with him. Gradually the boys come to terms with Bobby still being around but they are well aware that the longer his spirit lingers the sooner he'll become a Vengeful Spirit and they'll have to kill him again. Once things escalate, Bobby insists on them burning his flask to send him on, and the boys are faced with Bobby's death a second time.
Finding out what RRE was planning, Dean and Sam get their hands on an ancient stone tablet. When they break it free of the stone casing it was in, they awaken a prophet named Kevin Tran. Castiel, at this point, is awoken too but he isn't his normal serious self. The mess that was in Sam's head has turned Castiel crazy, leaving him frightened by conflict and more interested in speaking about flowers, bees, and honey than anything concerning the situation. This leaves Dean furious that Castiel is around but escaping his mistakes, and he lashes out at him, going so far as to say "Nobody cares that you're broken, Cas," because nobody ever cared that Sam was but Dean, and nobody ever cares when Dean is broken.
Kevin Tran, the prophet, is able to read what is written on the tablet and Castiel explains that it is one of many, written by the archangel Metatron, and it is in fact a Word of God. This specific one is entitled "Leviathan". With this, they learn how to kill Leviathan and prepare to do so. Once they've found their weapon to kill Dick Roman (and ultimately send him and all other Leviathan back to Purgatory) they head into RRE to get rid of him and to rescue Kevin after he was kidnapped by Leviathan. Breaking into the building by having Meg distract the guards by crashing the Impala through the glass display outside, Sam, Dean, and Castiel get inside and split up. Sam goes to find Kevin while Dean and Cas seek out Dick Roman. Finding him after a long search, they attack him with their weapon, the bone of a righteous mortal washed in the three blood of the fallen, but Dick explodes and takes both Dean and Castiel with him and his Leviathans to Purgatory, leaving Sam alone.
In Purgatory, Castiel's head is put right instantly and Dean is left alone when Cas flees. Frightened and alone, Dean is forced to fight. Season 8 shows that Dean becomes something primal and raw in Purgatory. He kills or he will be killed, he fights his way through Purgatory, demanding the location of "the angel" until he encounters a vampire named Benny who helps him fight off another few vampires. Benny explains that there is a way out of Purgatory for humans and that, if Dean wants him to show him the way, then Dean must take Benny's soul along with him. Teaming up with Benny, despite his wariness, Dean continues to slash and claw his way through Purgatory until they finally meet up with Castiel. Certain that Cas had been captured and not fled and left him, Dean hugs his friend when he sees him, relieved to have him around again, all past problems aside for the moment. It is then that Dean finds out that Castiel left him alone in Purgatory to supposedly protect him.
From here on out, the three of them fight their way through Purgatory to get to the portal that will get them out of there. Benny proves his loyalty to Dean countless times and Dean quickly forms a lasting friendship with him. However, Dean is single-minded. He wants only to get himself, Cas, and Benny home. Even Castiel's protests that the portal may not work for an angel fall on deaf ears and Dean continues to insist they'll all get out. Unbeknownst to Dean, Castiel doesn't actually want to get out of Purgatory, as he believes it is his punishment for the horrors he has committed. It is here that Dean will be coming to Mandalus, before performing the ritual to take Benny's soul into his arm, and before they all make a break for the portal.
All in all, Dean will come into Mandalus a more savage form of himself. It will take him a while to adjust back into normal life and he will be more distant with people to start with. Once he settles back in, Dean will be a lot more like his old, cheerful self. Forced to sober up in Purgatory, he drinks for recreation now, as shown in canon, rather than to drown his sorrows. He sleeps less, and is more alert, and more than anything he will be even more forcibly protective over his brother and his best friend. He will, however, be a little sterner and more world weary. His view on monsters has changed drastically after living amongst only monsters for a year, and he has learned that some monsters aren't bad, and that they don't choose to be what they are, and should all be given the fair chance if they haven't hurt anyone innocent.
Throughout season 7, the main antagonist is a monster known as the Leviathan. It is a biblical creature older than all creation. Leviathans are able to change into anyone once they've been touched by them and usually prefer to eat the original person to spare themselves any problems. The leader of these beings takes the role of a high class business man known as Richard "Dick" Roman, founder and CEO of Richard Roman Enterprises. Throughout the season, Dick is the source of constant problems (and a flurry of dick jokes) for the Winchesters, going so far as having two of his underlings masquerade as Sam and Dean and go on a killing spree in order of hunts that the boys did together since Sam left Stanford (meaning they started in the location in S1Ep1 and went onwards for several locations). Because of this, Sam and Dean were forced to deal with their dopplegangers and then had to hide the Impala and take on the fake names Tom (Dean) and John (Sam) Smith.
After dealing with their doubles, Sam discovered Dean had killed Amy. This set a strain on their relationship in which things between them become distant for a time, so much so that they go their separate ways, only to end up working the same case and getting roped into the situation together. It's here where Dean is contacted by Ellen Harvelle through a spiritual medium who tells him, again, to let go of his grief and guilt or it will kill him. Dean then apologises to Sam for betraying him and they hit the road together.
Shortly after that, Dean is faced with the distinct possibility of Sam leaving him for a normal married life. Despite the fact that Sam is drugged with a love potion and forcibly married (during their annual "Vegas Week", no less), he tries to be supportive until it comes to light that the whole thing is a sham. Still, this shows Dean is not prepared for the possibility of Sam leaving him behind, even if it means Sam will have a happy life with a woman he may love.
Following the wedding fiasco, and Sam's sham marriage being annulled, the two of them and Bobby get back to work on finding out what is happening at RRE. During this, Bobby is captured and the boys attempt to rescue him. As they are escaping, Bobby is shot in the head. Faced with the reality of their father-figure dying, both Sam and Dean handle it very differently. While Sam copes by making sure everyone who needs to know gets to know, Dean throws himself heavily into his work, trying to find out what is happening at RRE. It is during this time that the man who helped them cover their identities, Frank Devereaux, tells Dean that he can't keep running himself into the ground, and challenges him on the fact. The confrontation goes as follows:
Dean: I'm not going to quit. It's not even an option. I am not going to walk out on my brother.
Frank: Okay then fine. Do what I did.
Dean: What - go native? Stock up on C-rations?
Frank: No cupcake. What I did when I was 26 and came home to find my wife and two kids gutted on the floor. Decide to be fine 'til the end of the week. Make yourself smile because you're alive and that's your job. And do it again the next week.
Dean: So fake it?
Frank: I call it being professional. Do it right. With a smile. or don't do it.
Dean takes this advice to heart and, indeed, tries to do it right and be a professional. He is given a little time out (quite literally), when he's sent to 1944 to work a case with Eliot Ness concerning a time travelling god. It gives Dean some fun to be had in a bad time, perking him up quite a bit. The lifted mood helps Dean to get back into the swing of sleeping around but the woman he chooses (or is chosen by) for his first one night stand in years turns out to be an Amazon who uses Dean to give birth to an Amazon child, named Emma. Emma grows up in a matter of days to puberty at which point she is charged with killing her father to become a full-fledged warrior. Faced with his daughter, Dean tries to convince her to leave the Amazons and insists she hasn't killed yet and she doesn't need to. Instead, Emma tries to kill him and it is Sam who shoots her to protect Dean, putting both Sam and Dean on truly equal footing concerning Amy. Learning he had fathered a daughter and seeing Sam kill her took a lot out of Dean but he managed to bury the problem and move on, enjoying their next case (at Plucky Pennywhistle's Magical Menagerie where Sam is faced with his phobia of clowns and Dean gets both the chance to see his little brother covered in glitter and a giant rainbow slinky, thank you very much).
As their cases go on, Sam starts to succumb to his Lucifer hallucinations and Dean does what he can to help but it's a losing battle. Eventually Sam is checked into a hospital and Dean starts to look for a healer who might be able to fix Sam. It leads him into the path of a man named Emmanuel. It turns out that Emmanuel is actually Castiel without his memories, now married to a woman named Daphne who rescued him when she found him by a river without his memories. Emmanuel willingly comes with Dean to hopefully fix Sam. Shaken by the whole ordeal and still furious with Castiel for hurting Sam, Dean asks Emmanuel if he could actually be a bad person and simply not remember it, but Emmanuel says he does not feel like a bad person. Dean then explains that he is not able to forgive his friend Cas who betrayed him and caused Sam's illness. At the hospital, after meeting up with an old demon acquaintance named Meg, Emmanuel is forced to remember that he is Castiel in order for them to be able to get into the hospital and soon enough Castiel gets them in past the demons surrounding it, then taking on Sam's illness and remaining behind, insane and guarded by Meg, while Sam hits the road with Dean again.
Throughout the whole ordeal, Dean is emotionally weakened by seeing Castiel again and not really being able to take out his anger towards him. Having seen signs of things being moved around and having dealt with a haunting at a brewery, it is revealed that Bobby's spirit has been hanging around, attached to the flask that Dean carries with him. Gradually the boys come to terms with Bobby still being around but they are well aware that the longer his spirit lingers the sooner he'll become a Vengeful Spirit and they'll have to kill him again. Once things escalate, Bobby insists on them burning his flask to send him on, and the boys are faced with Bobby's death a second time.
Finding out what RRE was planning, Dean and Sam get their hands on an ancient stone tablet. When they break it free of the stone casing it was in, they awaken a prophet named Kevin Tran. Castiel, at this point, is awoken too but he isn't his normal serious self. The mess that was in Sam's head has turned Castiel crazy, leaving him frightened by conflict and more interested in speaking about flowers, bees, and honey than anything concerning the situation. This leaves Dean furious that Castiel is around but escaping his mistakes, and he lashes out at him, going so far as to say "Nobody cares that you're broken, Cas," because nobody ever cared that Sam was but Dean, and nobody ever cares when Dean is broken.
Kevin Tran, the prophet, is able to read what is written on the tablet and Castiel explains that it is one of many, written by the archangel Metatron, and it is in fact a Word of God. This specific one is entitled "Leviathan". With this, they learn how to kill Leviathan and prepare to do so. Once they've found their weapon to kill Dick Roman (and ultimately send him and all other Leviathan back to Purgatory) they head into RRE to get rid of him and to rescue Kevin after he was kidnapped by Leviathan. Breaking into the building by having Meg distract the guards by crashing the Impala through the glass display outside, Sam, Dean, and Castiel get inside and split up. Sam goes to find Kevin while Dean and Cas seek out Dick Roman. Finding him after a long search, they attack him with their weapon, the bone of a righteous mortal washed in the three blood of the fallen, but Dick explodes and takes both Dean and Castiel with him and his Leviathans to Purgatory, leaving Sam alone.
In Purgatory, Castiel's head is put right instantly and Dean is left alone when Cas flees. Frightened and alone, Dean is forced to fight. Season 8 shows that Dean becomes something primal and raw in Purgatory. He kills or he will be killed, he fights his way through Purgatory, demanding the location of "the angel" until he encounters a vampire named Benny who helps him fight off another few vampires. Benny explains that there is a way out of Purgatory for humans and that, if Dean wants him to show him the way, then Dean must take Benny's soul along with him. Teaming up with Benny, despite his wariness, Dean continues to slash and claw his way through Purgatory until they finally meet up with Castiel. Certain that Cas had been captured and not fled and left him, Dean hugs his friend when he sees him, relieved to have him around again, all past problems aside for the moment. It is then that Dean finds out that Castiel left him alone in Purgatory to supposedly protect him.
From here on out, the three of them fight their way through Purgatory to get to the portal that will get them out of there. Benny proves his loyalty to Dean countless times and Dean quickly forms a lasting friendship with him. However, Dean is single-minded. He wants only to get himself, Cas, and Benny home. Even Castiel's protests that the portal may not work for an angel fall on deaf ears and Dean continues to insist they'll all get out. Unbeknownst to Dean, Castiel doesn't actually want to get out of Purgatory, as he believes it is his punishment for the horrors he has committed. It is here that Dean will be coming to Mandalus, before performing the ritual to take Benny's soul into his arm, and before they all make a break for the portal.
All in all, Dean will come into Mandalus a more savage form of himself. It will take him a while to adjust back into normal life and he will be more distant with people to start with. Once he settles back in, Dean will be a lot more like his old, cheerful self. Forced to sober up in Purgatory, he drinks for recreation now, as shown in canon, rather than to drown his sorrows. He sleeps less, and is more alert, and more than anything he will be even more forcibly protective over his brother and his best friend. He will, however, be a little sterner and more world weary. His view on monsters has changed drastically after living amongst only monsters for a year, and he has learned that some monsters aren't bad, and that they don't choose to be what they are, and should all be given the fair chance if they haven't hurt anyone innocent.