Or outright stealing buffs from enemies and replicating them from allies. Bring a tank and you have yourself an OT. Bring a Bard and you have an extra burst dps. Half effect (double-AA Barrage as compared to triple), half duration. Finite charges available for theft, regenerating about one every 30 seconds, to a max of 4.
If you want the class (Thief) to be truly valuable / OP, just make it so you can only steal abilities you have cross-classed or else you can use steal to refresh the duration on an ability you already have by stealing it (refreshing half of the duration on Raging Strikes at full effect for the added duration).
You can also tag on an enmity-steal to that, and then place that enmity on someone else with another ability, 'Sabotage' or whatever.
If one still wanted to go with the item route (of 'Steal'), there would just have to be a way by which one could use basic items (healing and mana potions) for both damage and self-healing with a reduced CD on their use or else class-specific consumables (which likely would not actually take up inventory, being stored instead as buffs). If real consumables are used, Steal would basically keep your stock unlimited while in the dungeon, at the end of which the additional stock disappears.
