Adaptational Heroism: In the comic, Ipkiss gradually turns into a psychopath undr the influence of the Mask. In the movie, he is a much nicer guy, and his only "crimes" as the Mask are robbing a bank, messing with the police and eliminating the Big Bad. In the Animated Series, he is still not above trolling authority and people as a whole, but Stanley otherwise tries to use the Mask's power as a force of good, with relative success.
Adaptation Distillation: Though much of Ipkiss' personality is the same in the beginning of both the comics and the movie. In the comics Stanley becomes more psychotic and abusive whenever he doesn't have the mask on.
Butt Monkey: whether it's the comic, the movie or the animated series, Stanley tends to get treated like crap by almost everyone other than his closest friends, though he learns to stand up for himself as the film goes on. In the comic, that serves as his motive for revenge.
Chekhov's Gag - Stanley's favorite cartoons become the traits of the Mask (for starters, he spins like Taz).
Fusion Dance: Kinda. There is no dance involved, but in the animated episode "Split Personality", the Mask is split in two. In an attempt to see if it works, Stanley puts the half on. It works to say the least, resulting in a literal fusion of the two. One half Stanley, one half the Mask.
Large Ham: both as the Stanley and the Mask in the movie. In the animated series, Stanley is portrayed as a bit less hammy and more shy, but the Mask is still incredibly hammy.
Sexier Alter Ego - Note that he's not more physically attractive (unless you're into that sort of thing), but more confident and impulsive (and gets Reality Warper powers), and that's why he gets the Love Interest in the end.
Took a Level in Jerkass: His dislike of the Mask is completely justified in the comic, and while he is misguided Hero Antagonist in the movie, he overall does nothing the could be considered unreasonable. In the Animated Series, on the other hand, he keeps treating the Mask like a criminal and chasing him, not matter how many times he saw him save the day or arrest actually dangerous criminals.
Took a Level in Dumbass: Both a film-wise and adaptation wise. In his initial scene at the bank, he seems to be quite intelligent and competent. By the time we see him at the park, he's suddenly a ditz and by the film's end he's a certified idiot (though some of that may have been him being influenced by the Mask's power). The cartoon made him even dumber.
Angry Black Man - Lionel turned into one when Kellaway/Big Head started fighting the police, and challenged Big Head to a fist fight. Big Head almost killed him, and would have if Kellaway hadn't regained control of himself.
Karma Houdini: In the movie, since the scene of Peggy getting shoved in the printing press by Dorian and coming out as a bloodied newspaper that has her death on the front page was cut. She and Stanley became friends in the cartoon, on the other hand. But he never got over her selling him out.
Expy: He looks a lot like Eugene Rapaz, a drug dealer from the comics. Tone down the mohawk and replace the eye lenses with glasses...
Hammer Space: The tiny circular base of his head has the mechanisms to drive six small legs, a computer interface jack, various tools, a neural interface and circuitry, and one would assume a complex life support system to keep him alive without a body (albeit such a system may be meant for short term use as he's almost always attached to his robotic body).
Villain Decay: In his first appearance, he was a more or less serious and dangerous antagonist who came up with a relatively credible plan and almost killed Stanley. In later episodes, while he would still turn out to be a threat occasionally, his plans became more cartoonish, and he starts becoming more of a Butt Monkey like other villains.
Bad Ass: Both in the comics and the animated series, he is one of the few guys who can actually give the Mask/Big Head a run for his money.
Adaptational Badass: In the comic, he was incredibly strong and durable, but could eventually be taken down with enough beating. In the animated series, he is flat-out Nigh Invulnerable even to the Mask's supernatural powers, and can only be defeated by being sent away of trapt somewhere).
The Brute: More so in the comics than the cartoon, where he was a mob hitman and enforcer.
The Dragon: To Dr. Pretorius in the cartoon, to the mob in the comics.
Nigh Invulnerable: In the cartoon. In the comics he could be taken down with enough of a beating.
President Evil: A comic (likely based on the cartoon) had him running for Mayor of Edge City.
Self-Mutilation Demonstration: Just to be clear here- comic Walter can bleed, though it doesn't seem to really hurt him. Cartoon Walter is impervious to wounds. That said... in the comics he had a disgusting habit of cutting himself just to mess with people's heads.