New difficulty level: Masochist

Or "Punishing", "Ultra Hard", "IRL" whatever you want to call it. It would have the obvious tweaks to mob spawning, health, damage and so on, but as a kind of "escalation" you would now be required to have the appropriate tool to break a block or item, otherwise they are unbreakable, with very few exceptions. Axe for wood, shovel for sand and dirt, pickaxe for harder blocks, and you couldn't use one for the other. Falling into a hole without blocks or tools would be catastrophic, a lot of new unique challenges and strategies with this limitation while rendering old ones useless.