The vicious, murderous, insanely powerful, seemingly unbeatable and sometimes omnipotent Thanos... was once defeated by Squirrel Girl (as confirmed by the all-powerful Uatu the Watcher). That's right, the mutant known as Doreen Green whose powers give her squirrel-like abilities and the ability to control ordinary squirrels genuinely defeated the Mad Titan in 2005's GLX-Mas Special #1 (a Great Lakes Avengers comic). Thanos is powerful enough to begin with, so it would have been an impressive feat to defeat him on a normal day, but Thanos was actually empowered by the life-force of an entire planet at the time. No wonder Squirrel Girl has earned aliases like "The Anti-Life" and "The Slayer Of All That Breathes".
