Plague or WildWind are the best Spells for NON-Boss enemies. Plague has 
a good spread and a fair rate-of-fire, even with NO powerups, and inflicts
Poison. WildWind makes little snaking "cracks" of ice, damaging enemies 
anywhere on the screen! Forget aiming, WildWind will literally go anywhere 
good against enemies that actually fire back, IF you're lucky enough that 
the WildWind actually hits'em! Which one you use is completely dependant 
on playstyle: Plague is somewhat aimable, and inflicts Poison, while 
WildWind has a chance of Freezing enemies, preventing them from moving 
or firing.