Critical Fumble Chart

Critical Miss or Fumble Roll d20…
1	Your weapon takes critical damage making it potentially structurally un-sound. If you don’t repair it before your next critical miss or fumble, your weapon will break. Weapon user might suffer damage when weapon breaks. For magic spells To Hit, spell malfunctions and the result is damage to the caster or caster’s clothing or armor – DM can decide effects of the spell malfunction. A good rule of thumb is that the caster takes ¼ of the potential damage the spell would have done to the target.
2-4	Weapon is dropped in front of character in it’s a ranged weapon. Melee weapons that are swung might land d12 feet from character in direction of their swing. For magic spells To Hit, spell malfunctions and spell slot cast is lost – DM can decide effects of the spell malfunction.
5-8	Wild attack and miss! Your body is badly out of position because of your miss and any melee attackers in range will have Advantage next turn. Additionally, attacking next round will give you Disadvantage. Magic spells To Hit will fail and you lose the slot cast.
9-10	Your melee weapon is stuck in an opponent’s armor or in the ground. Thrown weapons fall back behind you. Ranged weapons fire but the ammunition does not leave the weapon. For magic spells To Hit, spell malfunctions and spell slot cast is lost – DM can decide effects of the spell malfunction.
11-14	You hit an unintended target with your miss. DM decides how this plays out.
15	You lose your footing on the terrain. Roll Dexterity / Acrobatics check (DC13) or fall prone. Your turn has ended and melee attacks have advantage on you (see p292 of PH for conditions of being prone).
16-18	In the heat of combat, something fragile – like a magic potion – you’re carrying breaks. DM determines which item and after effects of the breakage.
19-20	Weapon malfunction, DM’s choice based on weapon type. For magic spells To Hit, spell malfunctions and spell slot cast is lost – DM can decide effects of the spell malfunction.