34. Sabretooth
FIRST APPEARANCE: IRON FIST #14 (1977) Sabertooth started out as an enemy of Iron Fist, and after some brief encounters with Spider-Man, became recognised to most comic book fans as a major antagonist of Wolverine, even appearing in some comics as Logan's father. Much like Wolverine, he has a healing factor that causes him to be impervious to many injuries and attacks, and also has an extremely decelerated aging process. What differentiates him, however, is his extreme sensory perception, with enhanced sight and smell making him an even more dangerous predator. While, with his bushy eyebrows and claws for nails, it would be easy for a character like Sabretooth to seem silly and goofy, he is such a violent, animalistic threat to Wolverine that it's impossible not to take him seriously. Though his arrogance often gets the better of him and he is only blessed with an Adamantium frame in some comic book iterations (and even then, it's not up to Wolverine's standard), he can hunt and kill before most enemies even know he's there.
33. Doomsday
FIRST APPEARANCE: SUPERMAN: THE MAN OF STEEL #17 (1993) It's pretty much an instant claim to fame when you end up killing the Man of Steel himself, as this villain did in the famed comic The Death of Superman. Doomsday is essentially a base, primeval rage monster without a single facet of humanity, intent on causing as much pain and suffering as possible. The product of a cruel cloning process, Doomsday possesses the power to revive himself after death, but getting him there is itself quite an effort, given how resistant he is to attacks, and having a lack of internal organs to damage certainly helps. In addition to this, he is able to withstand tremendous environmental hazards, and can even survive Darkseid's Omega Effect, and possesses a seemingly unending level of stamina (he can fight Superman for a day without getting tired). One of his most famous acts, however, was fending off the Justice League by himself, and later, he would prove to be controllable thanks to Kryptonite, due to his obtaining some of Superman's DNA.
32. Sentinels
FIRST APPEARANCE: THE X-MEN VOL. 1, #14 (1965) The Sentinels serve important narrative functions in a number of classic X-Men comics, for they are robots designed to hunt down mutants and either capture them - often interring them in concentration camps - or just flat-out killing them. The Sentinels typically tower at around three-stories in height, can fly, project energy blasts, and can withstand massive amounts of damage from mutant enemies. Even when they appear to be destroyed, they are often able to reform or simply operate in a lesser capacity, making them vital tools for their more intelligent, calculating masters. Their most famous contribution to date has been in the comic Days of Future Past, where the Sentinels essentially rule the United States with an iron fist, an arc that is going to be adapted (in some capacity) in Bryan Singer's upcoming X-Men movie of the same name. We also briefly saw a simulation of a Sentinel in X-Men: The Last Stand, in the Danger Room.