I'm going to get the obvious nomination for Deadpool out of the way -
Deathstroke. Aside from the fact that both of them are mercenaries with accelerated healing, are armed with swords and guns, and were hired to take out a team of teenage superheroes, Deadpool is such an unsubtle knock-off of Deathstroke that their names (Deadpool = Wade Wilson; Deathstroke = Slade Wilson) are virtually identical. Sure, Deadpool's gone in a completely different direction over the years, but it seems like an easy pick.
---
Catwoman arcade ending:
Selina sets out to prove she's the best of the best when it comes to stealing, as we see a montage of her stealing from some of the best thieves in the Marvel universe (Gambit, the Prowler, Fantomex...) while leaving behind a calling card so they know who one-upped them. Her next target, Black Cat, catches her in the act (mostly, as Felicia admits, by thinking of what she'd do in the situation). The two banter back and forth before they start fighting - Black Cat may appreciate Catwoman's dedication to the theme, but she's not about to let Selina walk out with the priceless necklace that she used as bait.
The Joker arcade ending:
The Joker is holding try-outs for his next villainous scheme, though they aren't exactly going well - the
Circus of Crime has potential, but the Ringmaster insists on being in charge, which leads to the Joker dropping him into a pool of sharks. He likes what he sees of the
Death-Throws, but he decides to toss a lit bomb into their juggling act, which causes them to stop juggling and get as far away from the clown as possible before the bomb blows up. He eventually decides on a newly-formed version of the
Card Killers, because what kind of a deck doesn't have a Joker in it? And even if they die, there's
plenty more where they came from in this new universe!
(mostly, it's an excuse to show off as many obscure Marvel villainous groups as possible that fit Joker's motif)
---
(the design shown above is fanmade, but
his actual design is basically palette-swapped Darkseid; I figured something like this was more interesting than purple-and-teal Darkseid)
Unique Ability: Infinity Stones – unlike Thanos, Thanoseid’s unique action button lets him cycle through the Infinity Stones, with each one giving him a level 1 special. Once he uses the special associated with a given stone, the stone in question will light up; once all six are lit up, he can use his level 3 special.
Omega Beams – eye beams that randomly turn at at 90 degree angles, similar to Darkseid’s, though these are faster.
Boom Tube – much like Darkseid, Thanoseid steps back into a Boom Tube, appearing behind the opponent
Omega Stomp – similar to Darkseid’s Apocalyptic Stomp, Thanoseid leaps into the air and stomps on the opponent, though rather than jumping towards the opponent, he jumps up into a Boom Tube, coming out of another Boom Tube over the opponent’s head. (it can still be dodged, since the Boom Tube stays in one place, but it's harder to know when he'll land)
God Press – running forward, Thanoseid grabs the opponent and (if he connects) carries them until he slams them into the edge of the screen. This move is borrowed from Thanos, and also Omega Rugal.
Thanoseid Cutter – partially because it’s a reference to a classic SNK boss, and partially because I couldn’t resist the pun. Thanoseid jumps into the air, kicking in an arc over his head. This has a surprisingly wide range, deals a lot of damage, and serves as an anti-air.
Level 1 (with Power Stone): Omega Cannon – a pretty straightforward attack – Thanoseid fires a large red energy beam from his hand
Level 1 (with Space Stone): Omega Warp – Thanoseid shoots Omega Beams from his eyes, though before getting too far, they pass through a blue portal. More portals open up as the beam zips across each of them, making them even harder to predict than normal.
Level 1 (with Reality Stone): Fire Pits – Thanoseid warps reality so that fire pits appear on the ground, shooting up jets of flame before disappearing
Level 1 (with Soul Stone): Soul Drain – a grab move where Thanoseid lifts the opponent into the air, draining the life from them
Level 1 (with Mind Stone): Brain Drain – a grab move where Thanoseid lifts the opponent into the air, draining their special meter
Level 1 (with Time Stone): Fast Forward - Thanoseid accelerates time, gaining a significant speed boost for a short amount of time; the in-game timer also counts down faster while this is active.
Level 3: Anti-Life – now that he has gotten used to the power of the Infinity Stones, Thanoseid sees no reason to toy with his opponent any longer. Thanoseid shoots Omega Beams in front of himself, and if they connect, it starts a cutscene. With the power of the Infinity Stones, Thanoseid recites the Anti-Life Equation within the mind of every sentient being in the universe. As his opponent clutches their head, the screen fades to black with red stormy outlines as Thanoseid’s giant face fades into view, reciting bits and pieces of the Anti-Life Equation. (the different pieces of the equation overlap with each other, so it’s hard to hear what’s being said) When it is done, he makes a single command: “Die.” This move does so much damage that it’s difficult for it to not KO someone, though the match has likely dragged on for a while if it’s gotten to the point where he can use it.