Hey, for a first game jam it's a good start! In terms of being a platformer, it definitely is that. In terms of being a horror platformer, maybe a little less so. Honestly at first I thought it was gonna be a throwback to Scary Maze lol, not that I wanted that, but it would have been cute. I know the horror was in the twist at the end, but maybe making the visuals a bit creepier, or adding some subtle hints that hint towards the twist (monster footsteps, grunts here and there) could have helped a tiny bit.
The platforming feels good though! A little punishing to have to start from the beginning when you fall, but only a little. It wasn't that big of a deal, I'm just not a pro gamer and had to start over a couple of times :P