Sentinel

First Appearance: The X-Men #14

Created by Dr. Bolivar Trask, the Sentinels are a series of mutant hunting super-robots out to save humanity from the assumed evil homo superior. Though they have taken many forms and have had many masters, the standard Sentinel is about three stories tall, has AI that quickly learns from its opponent and is pretty tough, though by no means indestructible. MVC2's Sentinel is a little smaller, but he also possesses much of the strength, energy blasts, and limited flight capabilities of his brothers.

Servebot

First Appearance: Mega Man Legends (PlayStation)

Not merely one bot, but a big brotherhood of adorable rascals, the Servebots work for criminal Tron Bonne, helping her rob and steal. Despite this wrong doing, the Servebots don't really understand what they're doing, aside from innocently helping their boss. And they would do anything for her, no matter how badly she treats them. In MVC2 he's a comedic character, though also the smallest and hardest to hit, so don't laugh too hard.

Shuma-Gorath

First Appearance: Marvel Premiere #10

A bit of a Cthulu homage, Shuma-Gorath is a lord of chaos and one of the most powerful magical beings around. A planet threatening force, he has been pushed back just barely by the magical characters of Marvel, Doctor Strange mostly being involved. He has unlimited power, can change his body in any way, can teleport between dimensions and has an intelligence that borders on omniscient. So of course he decides to enter a fighting tournament.

Silver Samurai

First Appearance: Daredevil #111

This villain/occasional hero is from Japan and takes on the garb of their warriors, but in a much shinier way. The brother of one of Wolverine's many dead girlfriends, he's fought Wolverine as many times as he's helped him. A mutant, Silver Samurai can create a tachyon field, which he normally places around his sword and allows him to cut through anything, except adamantium. In addition to his prowess with the sword, he also has a ring the enables him to teleport great distances.

SonSon

First Appearance: Marvel vs Capcom 2 (Arcade)

Technically a new character, SonSon is the granddaughter of another SonSon who starred in the very early Capcom arcade game, SonSon. She fights to find a cure for an illness that struck her village, but that doesn't bring the cheery little monkey girl down. Her character is heavily inspired by the classic Chinese novel Journey to the West, which also inspired Goku in Dragonball, so don't think she's ripping him off. Such homages include the size changing staff, duplicating herself with hairs, and the use of a yellow cloud.

Spider-Man

First Appearance: Amazing Fantasy #15

Spider-Man is just your average guy with tons of problems, but routinely perseveres over incredible odds to save the day. Possessing the proportionate strength, speed, agility, and the ability to stick to surfaces of a spider, Peter Parker also has a spider-sense that warns him of danger. Plus he has web shooters of his own design that shoot webbing from his wrists. Though not formally trained, he has grown into a skilled opponent, learning as he's gone along. And Spidey will always be there to save the day, because with great power, comes great responsibility.

Spiral

First Appearance: Longshot #1

Kidnapped to the alternate dimension of Murderworld in the Mojoverse, she was trained to be a bodyguard and modified to have six arms, two of which are robotic. On top of being skilled with melee attacks, she is a strong mystic. She has cast spells on many heroes that have tried to stop her, even subduing the Avengers on one occasion. Additionally she's been known to help others with their cybernetic enhancements.

Storm

First Appearance: Giant-Size X-Men #1

Storm grew up an orphan on the streets of Cairo, until a chance encounter with Charles Xavier, who recognizes her potential. After being worshipped as a rain goddess in Kenya, she joins the newly reformed X-Men and quickly becomes one of their top members, even leading the team on occasion. Recently she became a Queen, marrying fellow African Hero Black Panther. With her power to control the weather, she can create the sublest wind or bury her enemies in a record breaking blizzard.