How does Thor lose this? Thor can travel (and send others) to different dimensions, command Mjolnir to seek out the real target among illusions, and Thor himself has resisted transmutation...and reversed it. This is really a stomp.
OP states no prep and do the death. Classic Gambit could charge inanimate matter with his eyes...so there's no reason he couldn't charge all the gear Batman wears and turn it into a Bat-shaped bomb. Gambit is too powerful to overcome without the prep.