I like the combination of orcs + life steal + green magic and more. It makes them feel like a unique group and I look forward to the full adventure!

Other folks have gotten to most of the mechanical stuff I would have said! I just want to add that, while I don't like the aging effect that comes with certain Talent strain effects because of how regularly you'll use those and how impactful they are, putting it on a villain is pretty cool, and "the year remains stolen" is a cool-as-hell bit of rules text!

I was tempted myself but I think avoiding the "See link for more..." trope is very important for a game jam and having it immediately downgrades my enjoyment.

Overall, there's some interesting ideas there but it really needs at least another round of cooking, editing, and testing, each.

Vaalyun

1. Characteristics seriously under par.
2. That's a lot for a signature to do. Recoveries are probably the most important resource a character has. And with no malice cost.
3. Effect on Slithering Green is redundant. And it probably should cost a bit of malice.
4. Kill for Me should be a maneuver.
5. Healing 20 Stamina just like that, regardless of how much damage, is FeelsBad. Also, kind of cheap.
6. Mossy Shield is cool.
7. Bloody Hammer or Hammer of Blood?
8. Pool is not explained well. I don't get it.
9. Taking away heroic resources really sucks. Surges, too but not as much. Regardless, VA 2 looks like a VA1.
10. "Of course" is redundant. Also, the entire VA3 makes no sense. You're sacrificing 5 monsters for... what?

Bola

1. Free strike underpowered for the level.
2. Godsblood sounds wierd. Looks to be confusing in run time. Maybe as a triggered action that costs malice instead of life.
3. My Storm looks underpowered.
4. My Manifold should be a maneuver. I don't see myself ever using this as a main action.
5. Could really use a malice ability and a triggered.

Fenn

1. Inertial Shield is a null reference and it also looks like a triggered. Should be a triggered.
2. What do you mean subject to the effect? Why not say that it's a free maneuver against dazed creatures?
3. Also, the Effect section on it is redundant.
4. Fenn moves how? How much? You can also just say that the damage enemies take is untyped.

Hammer

1. What do you mean can deal extra damage? How much? Which kind?
2. The description is convoluted and looks overpowered.

What a fun batch of baddies! There's some excellent ideas for abilities in here I'll definitely pull from for future encounters. Looking forward to the full adventure. Here's a few thoughts:

• Given the narrative of the Hammer of Blood, I wonder if Vaalyun's Replenishment ability should only be usable if he's attacked someone with the hammer that turn, as opposed to any damage dealt. Might add another interesting tactical layer to how he fights and how the players approach him as well. This isn't something I think is needed, just a light suggestion for your consideration. 
• The bonus damage of The Blood Hammer might not come up in some encounters, but could get crazy in others if the wielder gets their hand on a minion squad. Perhaps the bonus should be a pool that you can save up to spend on a strike rather than something that lasts the encounter?  It'd still scale well into the 5th level upgrade, since you can gift the pool to allies.