Ben 10 X Natasha Romanoff MCU
Heatblast
Stinkfly
XLR8
Ripjaws
Upgrade
Graymatter
Fourarms
Wildmutt
Ghostfreak
Diamondhead
Cannonbolt
Wildvine
Spitter
Buzzshock
Arctiguana
Blitzwolf
Snare-oh
Ditto
Upchuck
Waybig
eye guy
Frankenstein
Chromestone
Jetray
BigChill
Goop
Spider-monkey
Humungousaur
Echo Echo
Brainstorm
Swampfire
Alien X
Rath
Lodestar
Feedback
Ampfibian
NRG
Waterhazzard
Terraspin
Armodrillo
Chamalien
Ben Aliens above. No Ultimates
Adult Ben Tennyson is Transported into the MCU. (Ben can't Scan aliens from the MCU, And the aliens in his universe don't exist on the MCU So absolutely no one knows their strengths, weakness or even what species they are)
Only love interest is Natasha Romanoff.
He uses grey matter to hack the government and make all relevant documents.
When hacking he finds about SHIELD and HYDRA and knows that if he does go hero he can't reveal his identity.
He does go hero multiple times and without the time limit that he used to have his identity is never revealed.
SHEILD are extremely confused about all the different aliens that are saving people as they have no information on them, they only thing they know is that they seemed to all wear versions of the same suit. So they think it's a group of aliens working together.
He works with the Avengers in the Battle with Loki but he focused more on saving people using XLR8 to evacuate hundreds of people in minutes.
Fury tries to intimidate him into his identity and the identity of "his group" (Ben got a kick out of fury thinking he was multiple people) but he is nothing to a man that went up against the worst villian in his universe when he was 10 years old.
No matter what he doesn't join SHEILD as he doesn't trust the government.