Platformer Game Maker v4 It's rough.
But it's got potential. The available characters are interesting, and for the most part, fun to play with. I'd suggest adding onto this with other tools, and perhaps some premade traps, enemies, item to collect, etc. Part of the fun of a platformer is having some sort of goal, and then having things get in the way of achieving the goal. Adding the ability to further customize the characters, background, and music would also be a bonus.