82. Cassandra Nova
FIRST APPEARANCE: NEW X-MEN #114 (2001) Cassandra is a disembodied, parasitic astral life form known as a "mummudra", and is inextricably linked to Professor Xavier, essentially being his evil twin sister, most famous for ordering the Sentinels to murder 16 million mutants. As a result, despite being a relatively new villain, she has quickly become a fan favourite, and due to her unbreakable bond to Xavier, she is also gifted with all of his powers, as well as his potential to expand those powers. Furthermore, she is among the few mutants able to block out Xavier's telepathic abilities, and is able to mimic any other lifeform through its DNA. What's most interesting, for me, is the psychology of her character, the delusion she holds that her in-womb battle with Xavier is essentially the same as the yin-yang relationship they have on Earth.
81. Mister Mxyzptlk
FIRST APPEARANCE: SUPERMAN #30 (1944) One of Superman's best-loved foes, though not one who ever made it into the movies (unsurprisingly), the difficult-to-pronounce Mr. Mxyzptlk is an impish trickster who gets his thrills from taunting Supes, and though he generally isn't as malicious as most supervillains, he is more of a pest, one who can only be returned to the fifth dimension (for only a minimum of 90 days, mind) by managing to get him to say or spell his own name backwards. Mxyzptlk's powers are almost unlimited, and with a simple motion, he can do whatever he likes to try and humiliate Superman, though this never gets too dangerous as, ironically, Mxyzptlk values Superman's serious nature as ripe for pulling the best pranks. On the converse, Mxyzptlk is extremely gullible, and as a result, the seemingly contrived ritual of getting him to speak his own name backwards is actually remarkably easy. Though not the most menacing or cinematic of villains, there's absolutely nobody else like him out there.
80. Ultron
FIRST APPEARANCE: AVENGERS #54 (1968) Ultron is about to become a whole lot more popular in 2015 when he stars (as played by James Spader) in the next Avengers movie, Age of Ultron, but to comic book fans, he's been a classic supervillain for decades. Ultron isn't just blessed with the usual staple diet of superpowers such as heightened strength, speed, stamina, durability, and reflexes, but he can fire concussive blasts and put enemies into comas with his "encephalo ray". Oh, and he can perform mind control
and he is a super-genius. Ultron's exterior armour is popularly composed of adamantium, and some iterations of the character have even had him able to control hundreds of other Ultron suits, essentially forming a small army/hive-mind. The fact that Scarlet Witch is going to appear in Age of Ultron is telling, given that she's one of the few characters able to deal lasting physical damage to him.