Why is there no "mana steal" ability or item!?
Counterplay being the chiefest of idols, we ought to have this option when being dominated by a caster.
I think an active item that would "remove 50% of max mana" or maybe even instantly deplete mana would be a great way to counter fed casters in team fights. Of course it would require careful balance, but i think it would add a fun element.