Whenever you hit an enemy (and thunder mitts proccs), it finds all the enemies around that enemy (within a radius of 8m) and deals a lightning strike to every enemy in that radius. This deals damage and stuns every hit enemy for 3 seconds. This can be increased by the duration multiplier, but not with more copies.
There is a 10s cooldown between it being able to procc again.
The damage of the lightning strike scales with your level in game. This is what that looks like when it procs
Here's the formula for how much damage it does per hit enemy
$$
\text{Lightning Damage} = 3 \times \text{Thunder Mitts Copies} \times (8 + \text{Player Level}) \times \imagetooltip{Damage Multiplier}{https://res.cloudinary.com/dft1n3spr/image/upload/v1764501733/megabonk-guide/msyfbhopicnivvxuy6tk.png}
$$
Thunder mitts can deal crit damage.