Tony
A little corgi named Cody. He wears a little blue jersey with the name Stark on the back.

Steve
Bear, obviously...

Bruce
You wanted a bet so much but Bruce didn't. One day though he just came home with some duck that was abandoned and you guys named her Lily.

Pietro
He doesn't care if its illegal or not, he got a cheetah. Her name is Kanika which means African princess. You made a joke though that it wasn't fair that the pet only represented himself so the next day he got a turtle and you guys named it Speedy. Speedy and Kanika are the best of buds. :)

Bucky
You guys adopted a white kitten named Marshmallow. She grew up to be be fat, fluffly, and real sweet. You tease Bucky that he loves the cat more than you.

Thor
You got a goldfish named Sparky. Thor claims its one of the most fascinating things he's ever experienced, hell stare at it for hours.

Clint
Clint saved a baby Dove and you guys raised it to adulthood. Her name is Baby and she is the only bird you love.