Cast Plague of Vermin by paying {6}{B}, causing you to pay life equal to the highest life total your opponents have and create that many 1/1 Rat creature tokens.
Mirkwood Bats triggers for each token created this way, causing each opponent to lose that much life.
Each opponent loses the game due to having zero or less life.

Each opponent loses the game

Near-infinite creature tokens

Near-infinite ETB

Near-infinite lifeloss

Mirkwood Bats

Plague of Vermin

At the beginning of your precombat main phase, There and Back Again triggers, putting a lore counter on it.
There and Back Again's third chapter ability triggers, creating a legendary 6/6 Smaug creature token and causing you to sacrifice There and Back Again.
Mirkwood Bats triggers, causing each opponent to lose 1 life.
Kill the Smaug token, triggering its ability creating fourteen Treasure, fourteen Clue and fourteen Food tokens.
Mirkwood Bats triggers 42 times, causing each opponent to lose 42 life.
If desired, activate the Treasures by tapping and sacrificing them, adding fourteen mana of any color(s).
If you sacrificed the Treasures, Mirkwood Bats triggers fourteen times, causing each opponent to lose 14 life.

Academy Manufactor

There and Back Again

Activate Ashnod's Altar by sacrificing a creature token, adding {C}{C}.
Mirkwood Bats triggers, causing each opponent to lose 1 life.
Exquisite Blood triggers for each opponent.
Resolve the first trigger, causing you to gain 1 life.
Trudge Garden triggers, causing you to pay {2} to create a 4/4 Fungus Beast creature token.
Mirkwood Bats triggers, causing each opponent to lose 1 life.
Exquisite Blood triggers for each opponent.
Holding priority, repeat from step 1.
Resolve all remaining Exquisite Blood triggers, causing you to gain that much life, choosing not to pay for the Trudge Garden triggers in between.

Combos with "Mirkwood Bats"