If you had an imaginary friend, what did they look like? How did they act?

Fingers. He looked like my hand because I was a silly goober who thought imaginary friends were dumb, but had no issue with anthropomorphizing my own hand.

My imaginary friend was very tiny, and I'd imagine him cartoonishly jumping around whatever environment I was in so he could talk to me on my level. I used to hide out in the bathroom a lot, so oftentimes he'd be jumping on top of the toilet paper roll, then scampering up to the counter so we could have a proper conversation. If I was in the car, he'd sit on the edge of the window.

The best way I could describe him looking back would be like the vault boy from fallout. Not the same clothes or look, but just that cartoony style. I probably imagined him to be a little darker and with different colored hair.

Kiragushya a 2 1/2 foot tall dancing sword waving samurai

Weirdly, now I think about it, they were just me gender swapped

A blue Pikmin named Lure who would follow me around everywhere hahaha

I never had one as a kid either, not sure if I could have with being on the aphantasia spectrum. I do, however, have a lot of characters I've roleplayed with, and they all go by what one might say is a set system I use.