10 Insane Times Superheroes Lost Their Powers
4. Deadpool - Deadpool (Vol. 2) #52
Deadpool's entire life is based around his superpowers, as the continual life-threatening risks he places himself under time and time again are always with the knowledge that he can't be killed, so these stunts are technically entirely safe.
Until Deadpool #52, where the Merc With a Mouth is injected by his sidekick-turned-rogue Bob, and infected with a serum that disables his body's ability to continually heal itself. While Bob thinks this is part of his own master scheme, it's revealed that this was actually all part of Deadpool's, as the anti-hero had finally gotten tired of his superpowers and aimed to try and find a way to kill himself.
Proving that Deadpool is literally impossible to kill, his plan fails, as he realises he needs to save Bob from being murdered by half of the universe's underworld, after which point the serum wears off, rendering him invulnerable again.