Suggestion: Timer for spells

With new mana system some low level spells becoming overpowered, because they can be cast unlimited times:

True strike - gives +20 attack always, because can be cast unlimited times
Grease - same, and slow effect stacks...
Web, Spike growth, Entangle, Infestation of maggots etc.
I think all of those spells should be limited by timer for reuse (30 seconds, probably, should be enough)

Will look at this.