I have three pretty awesome ideas

1. An Empowerment spell, a necromancer (or mage) would hold a soul crystal (spell selected on the other hand) and when the spell is activated, the user would gain temporary ultra strength, kick spell, and immunity/resistance against most other spells (while slowly loosing mana), to make the spell's effect clear, the users eyes would glow purple, the spell should run out when the user is out of mana. However, after the is over, there should be a consequence like, maybe they pass out, become temporarily weaker to other spells, or become generally weaker (like when I human looses a lot of blood and has trouble standing).

2. A spell that disables another mages powers for a time, causes another mage to rapidly loose mana, or causes another mages spells to become temporarily dysfunctional. Example: A mage charges a lightning spell, but when they fire, they don't cast a spell but get a painful (but mostly harmless) shock, or ice spells just freezing their user.

3. The coolest spell. A spell of absolute evil, the user must be holding a large soul in a soul crystal, they will then activated the spell releasing a continuous beam of purple lightning that when in contact with a mage, will cause the mages soul and magical abilities to overload causing the mage to explode in an aura of purple light (that looks like the emp explosion light( but purple (it's actually an explosion radius) , the mage that had cast the spell will nearly die with severe burns, that no spell can heal (use a life syringe).