Card

Elvish Archdruid

Mana cost {1}{G}{G}

Other Elf creatures you control get +1/+1. {T}: Add {G} for each Elf you control.

Part of 72 known combos, 4 of them two-card. 2 official rulings.

Bracket

B1 Exhibition — Not in the same deck as its two-card combo partners: Staff of Domination, Umbral Mantle, Sword of the Paruns, Ringing Strike Mastery
B2 Core — Not in the same deck as its two-card combo partners: Staff of Domination, Umbral Mantle, Sword of the Paruns, Ringing Strike Mastery
B3 Upgraded — Not in the same deck as its early two-card combo partners: Staff of Domination, Umbral Mantle, Sword of the Paruns, Ringing Strike Mastery
B4 Optimized — allowed: No restriction beyond the banned list
B5 cEDH — allowed: No restriction beyond the banned list

Two-card combo with Staff of Domination, Umbral Mantle, Sword of the Paruns, Ringing Strike Mastery (early with Staff of Domination, Umbral Mantle, Sword of the Paruns, Ringing Strike Mastery)

Bracket: Lotus Vault analysis, with Commander Spellbook flags

72 known combos, 4 of them two-card.

Staff of Domination + Elvish Archdruid
Produces: Infinite card draw, Infinite draw triggers, Infinite lifegain
View on Commander Spellbook
Umbral Mantle + Elvish Archdruid
Produces: Infinite green mana, Infinitely large creature until end of turn, Infinite untap of creatures you control
View on Commander Spellbook
Sword of the Paruns + Elvish Archdruid
Produces: Infinite mana creatures you control can produce, Infinite untap of creatures you control, Infinite green mana
View on Commander Spellbook

2011-09-22 · Wizards of the Coast
Elvish Archdruid's activated ability is a mana ability. It doesn't use the stack and players can't respond to it.
2009-10-01 · Wizards of the Coast
Elvish Archdruid's first ability affects only other Elves you control. However, Elvish Archdruid's second ability counts all Elves you control — including itself.

Rulings: Scryfall · Wizards of the Coast