Card

Mana Echoes

Mana cost {2}{R}{R}

Whenever a creature enters, you may add an amount of {C} equal to the number of creatures you control that share a creature type with it.

Part of 931 known combos, 18 of them two-card. 3 official rulings.

Bracket

B1 Exhibition — Not in the same deck as its two-card combo partners: Sliver Queen, Myr Matrix, Eldrazi Displacer, Ingris Stingerquill, Dino DNA, Emiel the Blessed, Spawnsire of Ulamog, Retrofitter Foundry, Sprout Swarm, Pentavus, Ancestral Statue, Chrome Dome, Slimefoot, the Stowaway, Marneus Calgar, Fire Nation Archers, Cogwork Assembler, Kiora of Fire and Ashes, Ghave, Guru of Spores
B2 Core — Not in the same deck as its two-card combo partners: Sliver Queen, Myr Matrix, Eldrazi Displacer, Ingris Stingerquill, Dino DNA, Emiel the Blessed, Spawnsire of Ulamog, Retrofitter Foundry, Sprout Swarm, Pentavus, Ancestral Statue, Chrome Dome, Slimefoot, the Stowaway, Marneus Calgar, Fire Nation Archers, Cogwork Assembler, Kiora of Fire and Ashes, Ghave, Guru of Spores
B3 Upgraded — Not in the same deck as its early two-card combo partners: Sliver Queen, Myr Matrix, Eldrazi Displacer, Ingris Stingerquill, Dino DNA, Emiel the Blessed, Spawnsire of Ulamog, Retrofitter Foundry, Sprout Swarm, Pentavus, Ancestral Statue, Slimefoot, the Stowaway, Marneus Calgar, Cogwork Assembler, Ghave, Guru of Spores
B4 Optimized — allowed: No restriction beyond the banned list
B5 cEDH — allowed: No restriction beyond the banned list

Two-card combo with Sliver Queen, Myr Matrix, Eldrazi Displacer, Ingris Stingerquill, Dino DNA, Emiel the Blessed, Spawnsire of Ulamog, Retrofitter Foundry, Sprout Swarm, Pentavus, Ancestral Statue, Chrome Dome, Slimefoot, the Stowaway, Marneus Calgar, Fire Nation Archers, Cogwork Assembler, Kiora of Fire and Ashes, Ghave, Guru of Spores (early with Sliver Queen, Myr Matrix, Eldrazi Displacer, Ingris Stingerquill, Dino DNA, Emiel the Blessed, Spawnsire of Ulamog, Retrofitter Foundry, Sprout Swarm, Pentavus, Ancestral Statue, Slimefoot, the Stowaway, Marneus Calgar, Cogwork Assembler, Ghave, Guru of Spores)

Bracket: Lotus Vault analysis, with Commander Spellbook flags

931 known combos, 18 of them two-card.

Skirk Prospector + Pashalik Mons + Mana Echoes
Produces: Infinite colorless mana, Infinite creature tokens, Infinite damage
View on Commander Spellbook
Sliver Queen + Mana Echoes
Produces: Infinite colorless mana, Infinite creature tokens, Infinite creature ETB
View on Commander Spellbook
Ashling, the Limitless + Mana Echoes + Greenwarden of Murasa
Produces: Infinite creature ETB, Infinite creature LTB, Infinite colorless mana
View on Commander Spellbook

2020-08-07 · Wizards of the Coast
The creature entering the battlefield shares a creature type with itself if it has any creature types, so Mana Echoes usually adds at least {C}.
2020-08-07 · Wizards of the Coast
Mana Echoes counts the number of creatures that share a type, not how many types they share. For example, if a Human Warrior enters while you control two Humans and two other Human Warriors, you'll add five {C}.
2020-08-07 · Wizards of the Coast
The amount of mana to add is determined only as the triggered ability of Mana Echoes resolves. The ability isn't a mana ability; players may respond to it.

Rulings: Scryfall · Wizards of the Coast