52. Superman vs. Muhammad Ali
Remember the Champion from earlier on the countdown? Well, that is basically the plot of Superman vs. Muhammad Ali.
Some aliens want to have Earth’s best fighter fight THEIR best fighter or else they will invade and destroy Earth.
Both Superman and Muhammad Ali volunteer to do the fighting, and the alien leader determines that the two will fight on a planet with a Red Sun to determine who will fight the alien champion.
Well, naturally, Ali beats Superman badly (I mean, duh!), and he takes on the champion. Meanwhile, Superman (now recovered due to his healing powers) heads out and wipes out the alien invasion fleet while Ali takes care of the alien boxing champion.
However, the alien bad guy (Scrubb something) decides to back out of his word and still order an invasion, but his own champion turns on the leader for being dishonorable, and the bad guy is overthrown!