A weapon suggestion :) (COMMENT NOW :)

[IlPalazzo]

percentage mana dran could not be made cheap, as the 'damage' which would be done by the item would increase the higher the enemy tank is or at least the higher max mana the enemy would have

I don't understand. Normally spells scale with their level, so a high level tank has more mana, and the ability costs more, this makes the cost of the spell approximately a constant %, so if you want the mana drain to have a constant effect (i.e can cast one less spell) then you need to make it scale with capacity.

Otherwise, such an item would either be too strong early game, or completely useless late game.

% damage means it'll be useless early game, but too strong in the late game. It would make it another net - junk early game but much more cost effective late game when there's more money floating around and the abilities are worth blocking off. Constant damage instead of a constant % is better, because it'll force players to upgrade their mana drain to scale with the upgraded abilties upper tier tanks are given.

Having a "cast one less spell" effect wouldn't be a good constant to follow, because the abilities themselves aren't equal... If you deny a helicopter his missle ability he's unable to dish out 180-900 damage. If you deny a titan the ability to push out one of his abilties, he's unable to push out 1,000-5,000 (or much more considering his abilities are AoE). The problem here is that you paid the same amount of gold to ward off a <1000 damage spell from a 1,000 gold tank as you did to ward off a 1000-5000 AoE damage spell from a 25,000 gold tank. The second problem, is that more gold enters the game late game than it does early game. A % weapon wouldn't match the bounty system because it would mean the cost will be too expensive early game, but more manageable late game.