Actual Real Caveman
Terrarian
Terraria wouldn't be beatable as skyblock, but there could be some sort of "minimal world challenge" where there is literally only Hell, the Dungeon entrance, a small patch of Jungle, the Jungle Temple, and a tiny starting island. It would be pretty boring most of the time but the boss progression would be wack, like you wouldn't be able to do much in the way of ores.