I have absolutely no feeling for the balance here, so these may be useless...
Name: Force Exchange
Description: Drain life from the opponent but give some MP in return
Author: Virex
Requirements to summon: Int > 9, Wis < 15
Effect on target creature: Lose 1/3 HP rounded up, gain MP equal to 1/3 of casting creature's MP rounded up.
Effect on self: Gain HP equal to 1/3 of target creature's HP rounded up, lose 1/3 MP rounded up.
Name: Life exchange
Description: Drain energy from the opponent but give some life in return
Author: Virex
Requirements to summon: Wis > 9, Int < 15
Effect on target creature: Lose 1/3 MP rounded up, gain HP equal to 1/3 of casting creature's HP rounded up.
Effect on self: Gain MP equal to 1/3 of target creature's MP rounded up, lose 1/3 HP rounded up.
Name: Cruel exchange
Description: Exchange life and MP of the target.
Author: Virex
Requirements to summon: int > 13 or wis > 13 or cha > 13
Effect on target creature: future HP becomes equal to it's current MP, future MP becomes equal to current HP.
Effect on self: costs 8 mp.
And one that may not work at all:
Name: Thought exchange
Description: Exchange this ability for that of someone else.
Author: Virex
Requirements to summon: cha > 12
Effect on target creature: Creature loses 1 random ability and gains this ability.
Effect on self: Lose this ability and gain the ability target creature lost.
Edit: another set:
Name: Overload Gambit
Description: (can't think of a concise description)
Author: Virex
Requirements: Int < 7
Effect on target creature: For each stat, if that stat is higher then the caster's stat, the target loses 5 HP.
Effect on self: For each stat, if that stat is higher then the target's, you lose 5 HP.
Name: Madman's Gambit
Description: (can't think of a concise description)
Author: Virex
Requirements: int < 11, wis > 11
Effect on target creature: HP becomes 60 - 3 times your int.
Effect on self: HP becomes 60 - 3 times target's int.
Name: Sage's gambit
Description: (can't think of a concise description)
Author: Virex
Requirements: int > 11, wis < 11
Effect on target creature: HP becomes 3 times your int.
Effect on self: HP becomes 3 times target's int.