Selvala returned from the wilderness and brought all its fierceness with her.

Selvala, Explorer Returned

Parley — {T}: Each player reveals the top card of their library. For each nonland card revealed this way, add {G} and you gain 1 life. Then each player draws a card.

Secret Lair Drop

"The Lowlands refuse to suffer at the whims of the High City."

Bloomburrow Commander

Murders at Karlov Manor Commander

Dominaria United Commander

New Capenna Commander

Except in some very rare cases, the card each player draws will be the card revealed from the top of their library.

If you activate Selvala's ability while casting a spell, and you discover you can't produce enough mana to pay that spell's costs, the spell is reversed. The spell returns to whatever zone you were casting it from. You may reverse other mana abilities you activated while casting the spell, but Selvala's ability can't be reversed. You'll still have whatever mana that ability produced, and each player will have drawn a card.

Selvala's parley ability is a mana ability. It doesn't use the stack and can't be responded to.