Pause the game, go to "Extras", choose "Enter Code". Go to Gwenpool's room in the Avenger's Mansion. Enter the code on the computer in the room.

Code	Effect
4U9DAT	Vision (Civil War)
5G7HFS	Hulkling
7KDY3L	Vulture (Homecoming)
8KD3F6	Winter Soldier
BCR7QJ	Antman
BK9B3Y	Misty Knight
CDS278	Crimson Dynamo
CW9BRS	Spider-Woman
D6LJ4P	Songbird
G6K2VM	Hawkeye
GAVK9R	Giant-Man
HCE926	Maestro
HL7L7Y	Ragnarok
JD9GQA	Scarlet Spider
JDNQMV	Loki
LBYT59	Grandmaster (Ragnarok)
M68P3L	Captain Britain
NCMJU4	Hellcow
QG3VH9	Baby Groot Ravager
RMADXF	Spider-Man UK
S947TP	Darkstar
UUTZNC	Militant
XG7SAL	Green Goblin