For the sake of reference, here is a listing of all of Leonhardt's abilities. While he is not one to kill an opponent, this should outline why it is likely a bad idea to engage him in combat.
Reference video:
http://www.youtube.com/watch?v=nk0ZNks4BYQ,
http://www.youtube.com/watch?v=tlrLPZ66b2I and
http://www.youtube.com/watch?v=2Ef9qEfYTxw Warning, major first game spoilers first video, and second and third have major second game spoilers.
Physical factors:
-Insane speed. Even without arts he tends to get 2-3 actions per action a normal person can take. This also applies to casting arts.
-Good stamina. He definitely can take many hits without a problem.
-Good attack, also boosted by his ungodly sword that can cut through anything. He also very rarely misses. His attack power is definitely much higher than a normal opponent, so when he hits he hits hard.
-Good movement range, he can quickly close the distance between an opponent and himself.
-Resists pretty much every status effect except stat debuffs. So lowering his speed, strength and defense is possible, poisoning him or stunning him is not.
-He is nearly always holding back a lot of his true strength when fighting. Someone good at noting someone's ability may notice that his attacks seem unfocused or like he's not really trying. It is actually pretty hard to get a good read on his true strength because of this. But to give an idea if he's not holding back one bit, he can probably beat about any character in Luceti if he wanted to. He'd run into some trouble if a bunch of heavy hitters teamed up against him, but one on one he can handle most people.
Most of this isn't in the least bit supernatural, but there are some buffs from his orbment that exist and will be affected by the cap, but this effect is very minimal.
Arts (Magical skills):
-Of note, Leonhardt is an incredibly fast caster. Even the most powerful of arts he can finish casting within a matter of seconds at most usually.
Tearal - Heals a ton of HP, three uses of it brings him from 0 to full health. He also has access to La Tearal which is the same thing, but heals everyone in about a medium range (probably about 20 or so feet)
Earth Guard Mk 2 - makes him completely immune to the next two attacks no matter how powerful or weak they are. He also has access to the lesser version of this, Earth Guard which makes him only immune to the next attack.
Silver Thorn - affects a small area (about maybe 10-20 feet), a bunch of spikes come down in a circle and red lightning shoots around and does damage and confuses his opponents within the circle. If the person doesn't have protection against confusion it is going to confuse them nearly every time. It can be avoided if the person is quick enough to get out of the area he's casting it over before he finishes since it is centered over an area, not a person. Of note, canon is evil with the confuse status effect, the target of it will always either attack his allies or just move away from the enemy, more often attack allies. It is very very rare that they will actually attack the enemy (like a less than 1% chance it seems, slightly higher if there are no allies to attack).
Anti-Sept Zero - large range art that will cause the seal effect on anyone without protection against it. Seal basically prevents the use of magic, so it works much like silence. This covers most of the attack field in canon, so probably about a hundred foot radius or more.
Because of the way magic works in Trails in the Sky, if Leonhardt for some reason is lacking his battle orbment, he will be unable to use any arts or crafts. Of course, he is insanely paranoid and even sleeps and showers with it, so this is very unlikely to happen outside of his intro.
Crafts (Somewhat like magical abilities, but don't require casting):
Smashing Sword - A jumping attack where he smashes his sword down on the target. Can cause faint status (basically like a stun or paralyze status effect, target cannot act until it goes away). Works on a single enemy.
Zero Storm - A whirlwind attack that does damage and pushes people back. It also interrupts the casting of any arts. He only tends to use this when someone is casting and his turn comes up. Works on all enemies in a line. In canon this always interrupts, and any EP that would have been spent is not used. It basically causes a waste of a turn. If someone has protections against being interrupted while casting, then this won't be always effective and I'll leave it to player to decide if it works or not, but it should have a pretty high chance of working.
Demon Flame - His first S-Craft, basically he gathers up what is a combination of lightning and fire and then does a spinning attack that will affect a very large range (seems to be most of the field, probably about 100+ feet, if not more). Does a good amount of damage to anyone in range, pushes them backwards and induces the faint status effect a very large amount of the time. He can't use this every turn since craft points have to be recovered from attacking or taking damage, he regains at a high rate and can use this about every 2-3 actions.
Meiouken - His second S-Craft and this will likely not come into play unless someone really tough fights him. It is a freezing attack that covers nearly the whole field and does an immense amount of damage. Those who aren't KOed right off have a good chance of being frozen. Freeze status basically is a character literally being encased in a block of ice, unable to move and taking freezing damage each time their turn comes up (about 10% of health worth) until it either goes away or they are KOed too (and this status usually stays a long time, but it can be healed with any spell that removes all status effects). And warning, do not watch before or after the video's spot, major spoilers exist in it (especially before), unfortunately couldn't find a video of this that lacked spoilers.
Body-Split - See below, this one is so complex that it needs its own section. Note: Major spoilers exist before this video, so be wary going back on it.
On the Body-Split Craft:
-Leonhardt has no limit to the number of shadows he can make with this (I've seen 8 of them around in a battle before). It does take an action to create one, however, so he will waste a turn, of course with how fast he is, this isn't a huge deal. They do not affect his own HP or EP. Creating one does have a craft point cost, but he regains craft points quickly, so it won't bother him much.
-Their attack and defense is slightly lower than his own. They have his natural ability, but he cannot duplicate boosts due to quartz and the magical powers of his sword. Their attacks are not capable of penetrating armor and breaking barriers like his are.
-They have one third of his total stamina. This will change if he stops holding back to half his health.
-They resist any stat debuffs and status effects.
-They lack his insane speed and act at about the speed of a normal person.
-They can use any arts or crafts he can. However, he has to cast them himself and act through them so if he's fighting with them they will tend towards normal attacks because it is not easy to fight as more than one person and use complex arts and crafts. Zero Storm is an exception to this, if the conditions are met, the shadows will use that too.
-He can use them to stand in for himself. We saw two instances in canon where the protagonists were actually fighting one of his shadows, and even they are insanely powerful. He can see and hear through them and speak through them and even fight through them. He often will make use of them to be in two places at once, so don't be surprised if your character actually meets one of his shadows instead, he does use them outside of combat to accomplish mundane tasks that need to be done.
-They are not actually illusions. The damage they do is very real. They feel very solid and outside of seeing them vanish or seeing him with them (or seeing them do something insane like jumping off a balcony some few hundred feet up), it is nearly impossible to tell the difference between his shadows and himself. Basically consider them like him giving himself some extra members to his party, but they all look exactly like him. Also, a very observant person who has seen both him and the shadows may note that his sword is a slightly different color on the shadows, a more golden color whereas it is more reddish brown for him. (See
here and
here, first one is a clone, second is official art of the sword, credit to Misa for the images).
-Canon does not give a range for this, and the second time he uses one to stand in for himself was in a rather open area that was harder to hide in. The time limit would likely be until he has to sleep.
-The shadows cannot use this ability, even if he is using them as a stand in for himself. Since he so loves using it, this is another pretty big hint of when a shadow is standing in for him, but one would need to know he even has this skill to catch on to that.
-They will only vanish if brought to 0 HP, Leonhardt himself is knocked unconscious, or he otherwise dispels them. The act of them vanishing also does not affect his health.
And his second game stats:
HP: 31980, STR: 2000, DEF: 1333, ATS: 798, ADF: 798, SPD: 99, DEX: 999, AGL: 1, MOV: 6
(HP = hit points, STR=attack power DEF=defense, ATS=magical attack, ADF=magical defense, DEX=dexterity (determines accuracy), AGL=agility (ability to dodge attacks) MOV=movement range, SPD=speed (determines duration between actions, higher the number, the less time, so if his is far higher than someone he's fighting, he can easily attack two or three times before his opponent can act again)
The shadows:
HP: 15960, STR: 1599, DEF: 1199, ATS: 558, ADF: 598, SPD: 64, DEX: 999, AGL: 1, MOV: 6
And your party at level 99?
HP: 12711, STR: 1305, DEF: 970, ATS: 877, ADF: 60, SPD: 82, DEX: 29. AGL: 27, MOV: 5
HP: 11556, STR: 1457, DEF: 981, ATS: 870, ADF: 120, SPD: 88, DEX: 69, AGL: 42, MOV: 8
And the stats listed for the party are the two best fighters, and his shadows are their equals. This is why he's best handled with a group. He can be soloed, but you'll be healing every other turn and it still takes a ton of luck. And here he's still holding back to a slight degree because he becomes even more insane in the 3rd game.
And for my own reference, his likely quartz setup and other arts he has access to but rarely uses:
A picture of the setup Stats:
EP 5: Maximum EP+15% (Time*8, Space*8, Mirage*12)
Action 5: SPD+50%, MOV-2 (Time*12)
Cast 2: Significantly reduces casting time (Time*3)
Hit 5: DEX+25, AGL-5 (Mirage*12)
EP Cut 5: EP Consumption-50% (Time*7, Space*10, Mirage*7)
HP 5: Maximum HP+15% (Water*12)
Scent: Attracts monsters (Earth*2, Water*2, Fire*2, Wind*4)
Arts:
1. [Water] Tear - 5EP with that setup, heals 1000 HP in SC.
2. [Water] Teara - 10EP with that setup, heals 3000 HP in SC.
3. [Water] Tearal - 20EP with that setup, heals 6500 HP here.
4. [Water] La Tear - 10EP, heals 1000 HP, small circle AOE
5. [Water] La Teara - 28EP, 3000 HP, medium circle AOE
6. [Water] Revive - 15EP, revive a single target with 800 HP
7. [Water] Curia - 5EP. Cures all status effects except KO
8. [Water] La Curia - 15EP. See above, AOE
9. [Earth] Earth Guard - 5EP. Immune to the next attack
10. [Wind] Sylphen Guard - 5EP, AGL+50% for a single target.
11. [Wind] Sylphen Wing - 5EP, MOV+1 for a single target.
12. [Earth] Crest - 8EP, DEF+25% for a single target.
13. [Fire] Forte - 8EP, STR+25% for a single target.
14. [Mirage] Saint - 20EP, STR and DEF +25% for a single target.
15. [Space] A-Crest - 25EP, ADF+30% for one target.
16. [Time] Clock Up - 5EP, SPD+25% for a single target.
17. [Time] Clock Up EX - 15EP, SPD+50% for a single target.
18. [Mirage] Chaos Brand - 20EP, 100% chance of causing Confusion on one target.
19. [Mirage] Silent Cross - 25EP, interrupts arts and crafts... Hits ALL targets.
20. [Mirage] Silver Thorn - 45EP. See description above. Hits a medium-sized circular area.
21. [Time] Anti-Sept - 10EP, 100% chance of inflicting mute on a single target.
22. [Time] Anti-Sept All - 20EP, 100% chance of inflicting mute on all targets in a medium-sized circular area.
23. [Time] Oval Down - 50EP, reduces ADF by 30% and has a 100% of causing Mute. Hits all targets.
24. [Time] Clock Down - 25EP, reduces the speed of a single target by 50%.
25. [Earth] Stone Hammer - 5EP, hits a single target for Earth damage.
26. [Water] Aqua Bleed - 5EP, hits a single target for Water damage.
27. [Water] Blue Impact - 10EP, hits a single target for Water damage.
28. [Water] Blue Ascension - 15EP, hits a single target for... more Water damage.
29. [Water] Diamond Dust - 30EP, hits a small circular area for Water damage, 20% chance of freezing.
30. [Fire] Fire Bolt - 5EP, hits a single target for Fire damage.
31. [Wind] Air Strike - 5EP, hits a single target for Wind damage.
32. [Wind] Aerial - 10EP, hits a medium-sized circular area for Wind damage.
33. [Time] Shadow Spear - 20EP, hits a single target for Time damage, 20% chance of K.O.
34. [Time] Death Scream - 60EP, hits everything for Time damage and has a 20% chance of K.O.
35. [Time] Hell Gate - 15EP, hits a small circle for Time damage, 20% chance of causing Faint.
36. [Time] White Gehenna - 30EP, hits a medium-sized circle for Time damage and has a 20% chance of causing Faint.
37. [Time] Soul Blur - 5EP, hits a single target for Time damage and has a 20% chance of causing Faint.
38. [Space] Dark Matter - 20EP, hits a single target for Space damage. [Hits harder than the other single-target no-effect arts according to the wiki, hence the higher cost.]