Knight: I like the idea of a charge attack. I'll see if I can rip code from the Shield of Cthulu.
Berserker: Powerful, but punishing. Not sure I'll end up going with this but it's a solid idea.
Fortress: I've been thinking about having the ability Stone the fortress, giving huge damage reduction, and then gaining some sort of buff when coming out based on damage taken.
Sage: A personal spell could be good, I'll just need to figure out a progression and what type of spell to use. I'll want it to be interesting to cast, maybe requiring that you aren't hit for the ~1-2 sec casting time to work.
Warmage: I prefer the idea of consuming a chunk of mana to add damage to the weapon for a short period.
Conjuror: Sounds good. Any ideas for what kind of sentry?
Spirit Mage: It would have to last only ~5-10 seconds so that you don't get to just resummon without losing a considerable chunk of the buff legnth, but it's a good idea.
Contracted Sword: Hmmm, not liking these too much. Will want other options.
Wanderer: This would be iffy to get working. The minion could be a ~30 second thing, but the variety in fire rate makes % chance on hit a bad mechanic for something like this.
Marksman: Not a bad idea, and could see progression throughout the game. It could even use your own arrows to determine the type rained down.
Ranger: Hah, not likely. This wouldn't actually be too hard to do for some weapons like spears and boomerangs that are already projectiles, but swords would require an unreasonable amount of time and modded weapons wouldn't work.
Arcane Sniper: This is a possibility, but it would look kind of weird without some weapon to shoot from. I'd probably go with a variant of the Warmage ability.
Savage: That's a fun idea. The staff of earth is such an underused weapon, I could just take its projectile.
Ninja: If I can get a true invisibility working - one that prevents enemies from targeting you - that would be a good option.
Soulbound: I'd rather give the player the choice of what single minion to use.
Explorer: Simple and fitting, good idea.
Cavalry: Could be a little weird depending on the mount you're on.
Merfolk: Too hard, honestly. Minions that behave like NPCs are not easy to make, and I'd rather devote time to other things.
Werewolf: I'd considered this myself, though I hadn't thought about applying a penalty. This is a good idea.