What is your vote for the most overpowered spell in the game?

[Granamyr]

If we're still talking powerful, then I think Phantom wins above all others just due to its universal appeal. Fear has limits (plenty of monsters immune to mind spells) and seems more built around tactics whereas Phantom has something for everyone no matter what their strategy.

Overpowered, I don't think you can really make an argument that any spell is overpowered. Timeback is cost prohibitive and situational. Fear has a nice shutdown but it's also situational, limited and dependent on a high level army. Phantom comes pretty close given all of its positives with no apparent drawbacks...including moderate mana cost.

For damage, and I'm no pro mage, but I think:
1) Firestorm
2) Geyser
3) The rest

Haven't given Black Hole a shot but I think it will probably be the winner. I put Firestorm ahead because it has synergies with items and other spells and there are plenty of monsters that have a weakness to it. Igniting an enemy also adds damage and it's cheap. I haven't run the numbers but I'm guessing damage/mana spent has it coming out on top generally speaking and only scales up as you add weaknesses, items, medals, after-effects, etc. Black Hole will win the day though because there are plenty of ways to keep a high mana pool thus mitigating its high cost.