It isn't a solo game. The sprites for the character and the obsticles were done by https://thenri.itch.io/ . They just haven't accepted the invitation for co-admin yet. Glad you liked it! I honestly wanted to tone the difficulty down a bit towards the end but didn't find the time.
Edit: Seems like they did accept but I didn't check the "show as collaborator" box. Itch is really making this difficult '^^