What "thief" mechanics would work for League?

While some Champions might have a little "thief" vibe in their designs, only Trundle really gets the whole "stealing stuff" gameplay going. I say we need a Champion devoted to stealing, but I also want to know what mechanics might be considered off-limits by Riot.

We all know that stealing gold from another player's coffers would be 100% toxic, so that's out. But giving such a Champion a "Spellthief" passive would probably work as a substitute. As for other stuff, I have at least one idea for an ultimate...

(excepted from one of my Champion Concepts )

Severa dashes to target enemy Champion and drains X% of the target's attack damage and ability power for 6 seconds. Severa can activate The Big Heist again within 4 seconds to transfer the stolen stats to a target allied Champion for 6 seconds. If she does not reactivate it within 4 seconds, she automatically transfers the stolen stats to herself.

All stat modifiers decay over their respective durations.

Have a Jax out of control? Steal all his juicy offensive stats and turn his power against him! But be careful not to do that in Poppy's presence, or she'll just punt your teammate out of the fight! Balanced!

Would the above work? What else could work in terms of "thief" gameplay?