Shapeshifting (specifically into other people, like Mystique and Morph from
X-Men
, or like Changelings and Doppelgangers from D&D).
I could get into
anywhere
I wanted, with nobody realizing I'm not supposed to be there.
I could effortlessly disguise myself as anyone I wanted to take the blame or the credit for my actions, or even invent a brand new persona out of whole-cloth just for kicks.
I could con people into giving me free shit just because they think I'm a celebrity.
I could probably steal anything, spy anywhere, or harm anyone (physically or otherwise) I wanted to, and nobody would be likely to figure out it was me as long as I'm able to avoid capture before I can shapeshift again (the trick is to shapeshift into the desired form well in advance, wait for the cooldown to expire
before
doing the thing, and then shapeshift into a new form to get out of trouble) and am careful enough to avoid being seen shapeshifting.
I could tank anyone's reputation by stealing their identity and doing things that their families, friends, and/or fans hate.
I could even send powerful governments toppling down just by impersonating their leaders and torpedoing everything from within.
Even with the heavy nerf of a 24-hour cooldown between uses, this is
still
giving me
carte blanche
to go on an
unstoppable
crime spree. And that is, inevitably, what it will end up being used to do. It's like Plato's idea of the Ring of Gyges: absolute power of anonymity corrupts
anyone
absolutely.