png images and the fact that pk3 files are zip files would like to have a word with you:modding is impossible on mobile, you can make sprites and write code but when its time to package it all into 1 file you'll need slade. specially because for sprites they need to be .lmp which as far as i know cant be done on mobile, but as long as you can get someone to tackle the pc parts for you, you should be good
as far as i know the game cant modify the palettes of a png file so you'd be stuck with a green tails, and theres still alot of stuff that slade does thats necessary for modding.png images and the fact that pk3 files are zip files would like to have a word with you: