Titanic Trivia
An X-Men that can adapt to any strength got so overwhelmed by his power, his conclusion was to teleport away and never fight him.
Hulk
She Defeated Dormammu with an army of ghost squirrels.
Squirrel Girl
He was able to re-create spider sense and used it to defeat Spider-Man in Civil War.
Iron Man
He was created by M.O.D.O.K and (perhaps by accident) created Pym particles on one occasion.
Jeff the Land Shark
This duelist had a cat named Liho which is Russian for "misfortune".
Black Widow
He was beat by a wooden gun in the 1978 Fantastic Four Cartoon.
Magneto
This duelist defended his land from an invading army of skrulls, single handedly defeating a super skrull specifically born to kill him.
Black Panther
This duelist is the sorceress supreme of her Limbo dimension, where she beat Dr. Strange in a one on one.
Magik
His exoskeleton helped him absorb the blast from Ultron-Warlock.
Rocket Raccoon
This duelist was a member of Alpha Flight, The Avengers, The Defenders, The New Fantastic Four, X-Force, X-Men, and Weapon X.
Wolverine
He played baseball against a group of human souls being possessed by demons in order to free them from their possession (he wins btw).
Doctor Strange
This duelist was able to change his fighting style instantly, mid-fight, to beat Mr. X (a mind reader) in a unarmed duel.
Iron Fist
Taskmaster is terrified of fighting him after he flew his plane into a building to get him. He also hates cloning his fighting style, due to his habit of taking hits rather than dodging them.
Moon Knight
He was Thanos' only friend, and at one point gave the infinity stones sentience.
Adam Warlock
She canonically had a race change. The fans loved her new design so much they kept the change.
Psylocke
He has Allspeak. Anything he hears is automatically translated for him and anything he says can be understood by a group.
Thor
This duelist beat a phoenix-force buffed Namor and fenced off the Atlanteans in Avengers Vs. X-Men
Scarlet Witch
He killed all 350,000 inhabitants of a moon in order to stop the fallen one. (a herald of Galactus, similar to silver surfer)
Star Lord
He was responsible for showing Deadpool he was in fact in a comic book.
Loki
This duelist gets corrected by Doctor Doom when it comes to Star Trek trivia.
Spider-Man
In 1996's DC Vs. Marvel, Batman noted that he "could beat him, but it would take a long time."
Captain America
This duelist went toe to toe with Ghost Rider and won, with some help in his arsenal as well as a FULLY resisting Ghost Rider's penance stare.
Punisher
He was involved in the torture of Wolverine and then he later helped free him from his torture experiments.
Winter Soldier
She was able to take down Thor with a single strike.
Mantis
This duelist was a member of the Illuminati, the others being Iron Man, Black Bolt, Doctor Strange, Professor X, and Reed Richards.
Namor