I tried sticking to the vanilla DF creatures for the summons. There are no water-related element-men in the game... I can add a grimeling to the life/nature altar though.
Slowly approaching magic now: Vampire, Werewolf, Necromancer, Pyromancer and Geomancer are in the game. All have positive sides and negative sides.
Vampire:
- Insanely strong, never dies, good fighter.
- Might kill your own units when he gets thirsty.
Werewolf:
- Strong, transformes once every full moon or when fleeing combat, very hard to kill when transformed.
- Crazed, attacks everything in sight.
Necromancer:
- No need for food, drink or sleep; curses enemies and raises the dead.
- Animate dead might attack your lifestock or visitors; you also won't be able to use the corpses in reactions/butchering anymore.
Pyromancer:
- Throws fireballs, breathes fire, immune to exertion and fevers.
- Burns everything down, including allies, items, the surface, and potentially himself.
Geomancer:
- Breathes dust clouds and throws boulders. 50% damage reduction against everything.
- Might push allied units around with the dust clouds, moves at only 50% speed.
All of these are mutually exclusive, a Warlock can only ever be one of these.
Edit: Splint, you got your wish. Wishes. The necromantic buildings require less boulders; and you get a cheaper base worker unit for hauling/mining.