Boss stats
SPOILER WARNING, but seriously, duh. Why are you reading this if you haven't played the game (unless you are Snow)? Go play the game.
Unshockingly, since it's a Suikoden game, most of the bosses are pretty bad (both in-game and in the DL). This makes me lazy about collecting stats. As it has everyone else apparently. So yeah. This is a terrible boss stat topic by my standards, and you'll all have to deal with it, or make better notes yourselves.
I haven't tested boss speed too extensively, generally assume they're all pretty close to average unless I say otherwise.
I don't have Conon and Fergus stats. They aren't very good, doing ST evadable 3HKO off slightly sub-PC durability. Woooo! Conon has a low 3HKO off above average speed, Fergus a high 3HKO off below average speed, from memory. It's possibly I'm underrating them a little and Fergus actually 2HKOs or something but whatever. Both Lights. Someone else can grab stats for them. There's also Dirk I guess, who is probably in the same general area and might even prefer his skill-less PC form but is screwed either way.
A whole bunch of PCs also have boss forms, often more than one! (Diadora, Sophia, Nova, Vaslof, Resno, Fredegund...) Due to their general mediocrity and unmemorability (discounting the ones which are plot fights), I'd imagine the PC forms will be seen as both more legal and, usually, better.
I think all techs are ITE. Actually, I don't think I've ever seen a boss miss, but missing in general is rare as hell in this game, so who knows. Also, I make up names for enemy-only techs, but everyone should know this by now.
I don't have party stats for one to compare bosses to, but in general... endgame damage is ~1500 and HP is just shy of 500 according to the stat topic. This probably works well enough for the final boss on the whole, with the second to last being only a little better. The bosses in Cynas (third to last dungeon) should be a bit better off both due to lower levels but also because chances are you may not be able to afford lots of really uber storebought gear yet (those Giant God Fists and their +100 HP are silly) and characters haven't learned their last two skills. So they probably face an HP value in the lower 400's and maybe 20-25% less damage. That said, I pretty much encourage players to use their personal judgement here.
Macoute
Windbag
~7500 HP
Below average Def, good MDef. Def isn't far from average (+10%?), but the MDef is somewhat notable (~1/3 reduction?). Didn't test exactly.
Physical: ~160 damage
Angel Song: ~100 magic damage MT, 50% silence, 50% sleep
Comments: Competent by Tierkreis boss standards, and probably the best Suikoden human boss since S3! Both of these say NOTHING. Macoute's damage and durability (particularly physical) are unimpressive at best, but Angel Song is a good move in-game and not bad in the DL either. If you don't resist the status and fear silence, Macoute only needs one turn to fuck you over. Middle.
Beardsley (Cynas form)
Jade lookalike
~5500 HP
25% Weak to Slash
Physical: ~150 damage
Comments: He's terrible. I guess since he's in the middle of a dungeon with no save points nearby the designers went easy on us, or something. It's possible he has other moves since I didn't draw the battle out (and his HP uh sucks even going easy on him) but FAQs don't mention them, so whatever. Really didn't need the slash weakness either. Light.
Valfred (Cynas form)
Fundamentalist
~6000 HP
Physical: ~130 damage, long range
Bind Lightning: ~180 magic damage, unknown chance of paralysis (0/1 for me)
Fuse Dome: ~200 magic damage MT
Notes: Fights with a Gigas Arms who has ~3000 HP, is protected in the back row, and can physical for ~120. I killed it first so unsure if it needs to be killed to end the battle.
Comments: The depressing thing is that Fuse Dome (solid 3HKO MT, probably 2HKOs some people) is very good for a Tierkreis boss up to this point. Other than that, the durability is too bad to win slugfests against much of anything. In an earlier form, he had a move that did sleep+paralysis+damage (ST) which is way better in a duel than anything he has here, and it's possible he still has it in this form, which would make him quite a bit better if the status accuracy is good. He doesn't want the previous form since its durability is epic (even compared to this one). Assuming possible hype there doesn't pan out, Light. Doesn't matter unless one bans....
Valfred (final dungeon form)
"This one day! It's everything to me!"
~10000 HP
25% Weak to slash. High Def (~30% reduction). Above average MDef.
Physical: ~160 damage.
Heavy Slash: ~300 damage.
Counter Stance: Counters regular physicals this round, dealing ~160 damage each time. The counterstance is active for the entire round regardless of speed.
Notes: Good defence basically cancels out his slash weakness, so in practice he's resistant to everything but slash.
Comments: Totally unlike his previous forms, Valfred has opted for a pure physical build, and it's a winning trade. Heavy Slash is quite painful, scoring easy 2HKOs, and his durability is actually... okay it's still mediocre, but better! Maybe above PC against non-slashing physcials even! Middle, maybe even a pretty solid one, he's like... a less ball lightningish Culgun or something. Yay?
The One King
One world, one future
Notes: The One King has three forms. After the first, the battle ends and you gain exp from the fight, possibly levelling up (and fully healing HP/MP as a result). After the second, the battle ends, then another one immediately begins. Status effects are removed between these battles, and I'd bet that anyone dead revives to 1 HP, but you gain no Exp/HP/MP otherwise. Then there's form 3. In other words, 2->3 has an argument to be a legal formchain (though not one I personally swallow) whereas 1->2 does not unless you're really generous. Still, here they all are.
All forms of the One King appear to have slightly above average speed.
First form
~12000 HP
Average defences.
Physical: ~200 damage, long range
Comments: Oh no, ST 3HKO off average durability. Pretty much a pure average dueller with boss immunities, he'd have to try to be more boring. LONG RANGE SPOILS FIRE EMBLEM.
Second form
~15000 HP
Slightly above average defences.
Physical: ~220 damage to a column
Summon Giant Rock: ~140 physical damage MT
Comments: Getting closer to 2HKO now, but not quite there yet!
Third form
~25000 HP
Reduces physicals by ~10%, magic by ~20%.
Physical: ~220 damage to a column
Mjollnir: ~330 physical damage, long range
Shield: Ups own physical defence for 5(?) turns. About a 40% reduction on top of his existing defences.
Perfect Unity: ~330 (unknown damage type) damage MT. Usable below half HP only.
Comments: I still need to test what damage type his ultimate attack is, and how long Shield lasts. Mjollnir's almost as good in the DL anyway, and in-game is notable because it can OHKO a frail back-row healer (*grumble*). Durability hovers a bit over 2PC, the def-buffer is nice if he expects to live 3 more turns against a physical opponent, and he solidly 2HKOs off decent stats all-around. No real flaws, although if his big attack ends up physical he becomes quite wallable. Even so, a good overall mix. High Heavy.