Mortuary + Goblin Bombardment + Bolas's Citadel + Haywire Mite

Mortuary

Goblin Bombardment

Bolas's Citadel

Haywire Mite

How it works

1. Activate Goblin Bombardment by sacrificing Haywire Mite.
2. When Haywire Mite dies, it and Mortuary triggers.
3. Resolve the Mortuary trigger, putting Haywire Mite from your graveyard onto the top of your library.
4. Resolve the Haywire Mite trigger, causing you to gain 2 life
5. Resolve the Goblin Bombardment ability.
6. Cast Haywire Mite from the top of your library by paying 1 life due to Bolas's Citadel.
7. Repeat.

This elegant loop turns Haywire Mite into an endlessly recurring ammo source, letting you sacrifice it to Goblin Bombardment to deal damage while effortlessly offsetting the life cost. Whenever the Mite hits the graveyard, Mortuary steps in to instantly place it right back on top of your library. From there, Bolas's Citadel allows you to recast the creature using your life total instead of mana, and since Haywire Mite triggers its own lifegain ability upon dying, you even break even on life to keep the loop going indefinitely.