Long-story short, I did a TF challenge with New Super Mario Bros where I had to play through the whole game without using powerups, but if I died from an enemy at all, the run would end and I would have to draw myself being transformed into the enemy that killed Mario in the way that it happened.
More info can be found here:
https://twitter.com/TransformYosh/status/1499475308298309635?t=X7ZyTptQA4F-Lno3gi1Vqg&s=19

I ended up losing to Mummipokey in W2-Castle, so now I'm becoming one!

Also, I cannot find any sort of Mummipokey TF of any kind anywhere, so this may very well just be the first one (barring the FA upload of this same picture) :}