Card

Devoted Druid

Mana cost {1}{G}

{T}: Add {G}. Put a -1/-1 counter on this creature: Untap this creature.

Part of 367 known combos, 15 of them two-card. 2 official rulings.

Bracket

B1 Exhibition — Not in the same deck as its two-card combo partners: Swift Reconfiguration, Hazel's Brewmaster, Machine God's Effigy, Tyvar, the Pummeler, Tayam, Luminous Enigma, Mikaeus, the Unhallowed, Quillspike, Bristly Bill, Spine Sower, Myrkul, Lord of Bones, Vizier of Remedies, Luxior, Giada's Gift, Haldir, Lórien Lieutenant, Hexavus, One with the Stars, Captain Rex Nebula
B2 Core — Not in the same deck as its two-card combo partners: Swift Reconfiguration, Hazel's Brewmaster, Machine God's Effigy, Tyvar, the Pummeler, Tayam, Luminous Enigma, Mikaeus, the Unhallowed, Quillspike, Bristly Bill, Spine Sower, Myrkul, Lord of Bones, Vizier of Remedies, Luxior, Giada's Gift, Haldir, Lórien Lieutenant, Hexavus, One with the Stars, Captain Rex Nebula
B3 Upgraded — Not in the same deck as its early two-card combo partners: Swift Reconfiguration, Hazel's Brewmaster, Machine God's Effigy, Tayam, Luminous Enigma, Bristly Bill, Spine Sower, Myrkul, Lord of Bones, Vizier of Remedies, Luxior, Giada's Gift, Haldir, Lórien Lieutenant, One with the Stars, Captain Rex Nebula
B4 Optimized — allowed: No restriction beyond the banned list
B5 cEDH — allowed: No restriction beyond the banned list

Two-card combo with Swift Reconfiguration, Hazel's Brewmaster, Machine God's Effigy, Tyvar, the Pummeler, Tayam, Luminous Enigma, Mikaeus, the Unhallowed, Quillspike, Bristly Bill, Spine Sower, Myrkul, Lord of Bones, Vizier of Remedies, Luxior, Giada's Gift, Haldir, Lórien Lieutenant, Hexavus, One with the Stars, Captain Rex Nebula (early with Swift Reconfiguration, Hazel's Brewmaster, Machine God's Effigy, Tayam, Luminous Enigma, Bristly Bill, Spine Sower, Myrkul, Lord of Bones, Vizier of Remedies, Luxior, Giada's Gift, Haldir, Lórien Lieutenant, One with the Stars, Captain Rex Nebula)

Bracket: Lotus Vault analysis, with Commander Spellbook flags

367 known combos, 15 of them two-card.

2018-12-07 · Wizards of the Coast
You put the -1/-1 counter on Devoted Druid as a cost to activate its ability, not when it resolves. If paying the cost causes Devoted Druid to have 0 toughness, it's put into your graveyard before you can untap it and before you can even pay the cost again.
2018-12-07 · Wizards of the Coast
If you can't put -1/-1 counters on Devoted Druid (due to an effect such as that of Solemnity), you can't activate its second ability. If you can put counters on it, but that is modified by an effect (such as that of Vizier of Remedies), you can activate the ability even if paying the cost causes no counters to be put on Devoted Druid.

Rulings: Scryfall · Wizards of the Coast