I've fused some Binding of Isaac bosses/enemies with Pokémon! I even fused a couple of the starters from Pokémon Scarlet and Violet. Take a look!
I started off by drawing them in black and white (6 colors, painterly pixel style) Then I animated them by squishing and smearing stuff around.
Then I colored them by replacing the 6 color ramp in select parts of the images (usually the fusion is a different color)
Then I added some effects in post! Voila!
I hope you enjoyed. Which was your favorite?
The Binding of Isaac Rebirth - Diptera Sonata