This played out very well, it was quite fun
A few things though:
One, sometimes when i was jumping, the characters legs would separate from the top half of their body by a little bit, so it looked kinda weird.
Two, in the Tankman level, if you go all the way to the right with Bitey, its possible to go entirely off screen, thus pretty much forcing you to restart the level, so you might want to fix that.
Three, when i was collecting items in the Pico level, there were 2 items that seemed impossible to get: Salad Fingers' spoon, because you placed it in such a way that only Pico could fit in, but it was on invisible blocks, so only Salad Fingers could stand on them. And then Dad's skull. I tried both starting the level with him and also trying to backtrack from the checkpoint, and with Dad's size, both were pretty much impossible, the platforms blocked me from moving.
Four, during the boss fight with P-Bot, when i was attacking him with each of the characters, i had no idea if i was doing any damage to him or not, there was no clear sign of P-Bot taking damage, that is until the next character dropped in, so until that point, i just had to keep on attacking, hoping i was doing damage. It'd be nice if maybe P-Bot flashed or something when he took damage so i'd know when he was hurt instead of just attacking wildly, hoping im doing damage.
Besides those 4 things though, this was immensely fun to play, I loved the different stages and the music set to each one, and the different way each character played. Great Job and Happy Pico Day!