Curses:
Focused on controlling the enemy (move/attack/cast speed slow, interrupts, mana burns...) And on dots.
Blood magic (if necromancer doesn't get something similar):
Sacrifice hp (either yours or allies') to damage enemies, self-inflict bleed to poison a large area, steal enemies' hp...
Support:
Not so sure about this one
Should not be the best healer, but should offer a wide range of buffs and heals at a cost.
Maybe heal by sacrificing your own hp to heal other, but have a way to siphon hp from healthy allies?