Card

Marrow-Gnawer

Mana cost {3}{B}{B}

All Rats have fear. {T}, Sacrifice a Rat: Create X 1/1 black Rat creature tokens, where X is the number of Rats you control.

Part of 9 known combos, 3 of them two-card. 1 official ruling.

Bracket

B1 Exhibition — Not in the same deck as its two-card combo partners: Thornbite Staff, Intruder Alarm, Faces of the Past
B2 Core — Not in the same deck as its two-card combo partners: Thornbite Staff, Intruder Alarm, Faces of the Past
B3 Upgraded — Not in the same deck as its early two-card combo partners: Thornbite Staff, Intruder Alarm, Faces of the Past
B4 Optimized — allowed: No restriction beyond the banned list
B5 cEDH — allowed: No restriction beyond the banned list

Two-card combo with Thornbite Staff, Intruder Alarm, Faces of the Past (early with Thornbite Staff, Intruder Alarm, Faces of the Past)

Bracket: Lotus Vault analysis, with Commander Spellbook flags

9 known combos, 3 of them two-card.

Marrow-Gnawer + Thornbite Staff
Produces: Infinite creature tokens, Infinite creature ETB, Infinite creature LTB
View on Commander Spellbook
Marrow-Gnawer + Intruder Alarm
Produces: Infinite creature tokens, Infinite mana creatures you control can produce, Infinite untap of creatures
View on Commander Spellbook
Marrow-Gnawer + Ashnod's Altar + Sword of the Paruns
Produces: Infinite colorless mana, Infinite creature tokens, Infinite death triggers
View on Commander Spellbook

2004-12-01 · Wizards of the Coast
Marrow-Gnawer's ability counts the number of Rats on the battlefield when it resolves, so you don't count the sacrificed Rat.

Rulings: Scryfall · Wizards of the Coast