There’s a house rule I run into a lot in D&D groups that a natural one on a d20 roll results in either some horrific result, rolling on a table for fumbles, or even simply giving the enemy an Opportunity Attack against the attacker.
While I enjoy fumbles and craziness in some game environments, I don’t find that modern D&D games as a whole mesh well with the gonzo aesthetic of the crazy fumble and critical charts from Rolemaster or Dungeon Crawl Classics. In fact, the fumbles in DCC (along with the swinginess of spellcasting) is one of the main reasons that while I love the game, I wouldn’t be content to play it as my only fantasy RPG system.
But there’s always people asking about people’s critical fumble tables. So here’s my new 5e critical fumble table for combat (roll 1d8 whenever you roll a 1 on an attack roll).
Because really… fumbles belong in comedy games – and a top efficiency fighter in 5e can have as much as a 33% chance of fumbling in a round of combat, assuming said fighter is not under the effects of a haste spell, which would increase the chances another 10% or so.