Pause the game, go to "Extras", choose "Enter Code".

Code	Effect
4U9DAT	Vision (Civil War)
5G7HFS	Hulkling
7KDY3L	Vulture (Homecoming)
8KD3F6	Winter Soldier
BCR7QJ	Ant-Man
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