Goblin Sharpshooter + Splinter Twin

Prerequisites

Splinter Twin attached to Goblin Sharpshooter. Goblin Sharpshooter does not have summoning sickness. You have a way to cause a non-Goblin Sharpshooter creature to die (for an additional result).

Steps

1. Activate Goblin Sharpshooter's ability from Splinter Twin by tapping it, creating a token copy of Goblin Sharpshooter with haste.
2. Activate the token copy of Goblin Sharpshooter by tapping it, dealing 1 damage to itself.
3. The token copy of Goblin Sharpshooter dies, triggering the nontoken Goblin Sharpshooter, untapping it.
4. Repeat.
5. Alternatively, if you have a way to cause any creature besides the Goblin Sharpshooters to die, for instance by targeting a 1-toughness creature in step 2, you can untap Goblin Sharpshooter an additional time and repeat step 1 one additional time before continuing the combo.
6. This will leave you with one additional surviving Goblin Sharpshooter token, which can activate itself once per loop for infinite damage to any targets.