
Creature — Spirit
Untap all permanents you control during each other player's untap step.
2/4

Untaps your lands each end step for similar mana availability.

Untaps creatures during each other player's untap step like Seedborn.

Untaps all lands and creatures during each upkeep, symmetric ramp engine.

Untaps a big permanent each turn for repeated mana/abilities.

Untaps all lands after attacking for extra mana.

Untaps all lands on combat damage for double mana.

Triples mana for green ramp payoff like Muse's extra mana.

Untaps your lands while taxing opponents, big green mana engine.
All your permanents untap during each other player's untap step. You have no choice about what untaps.
Other effects can prevent a permanent from untapping during an untap step. You do need to look carefully, however, as many effects say that the permanent does not untap during its controller's untap step, and this card's ability occurs during other players' untap steps. If a card does say this, then Seedborn Muse can untap it. But some other abilities are not written this way and can still prevent a card from untapping.