Mockery of Nature

Emerge represents two static abilities that function while the spell with emerge is on the stack. “Emerge [cost]” means “You may cast this spell by paying [cost] and sacrificing a creature rather than paying its mana cost” and “If you chose to pay this spell’s emerge cost, its total cost is reduced by an amount of generic mana equal to the sacrificed creature’s mana value.”

If you cast a spell for another cost “rather than paying its mana cost,” such as an emerge cost, you can’t choose to cast it for any other alternative costs. You can, however, pay additional costs, such as kicker costs. If the spell has any mandatory additional costs, those must be paid to cast it.

Once you begin to cast a spell with emerge, no player may take actions until you’re done. Notably, opponents can’t try to remove the creature you wish to sacrifice.

Colored mana components of emerge costs can’t be reduced with emerge.

You may sacrifice a creature with mana value greater than or equal to the emerge cost. If you do, you’ll pay only the colored mana component of the emerge cost.

If you sacrifice a creature with {X} in its mana cost, that X is 0.

The mana value of a creature spell with emerge isn’t affected by whether its emerge cost is paid. For example, if you cast Decimator of the Provinces for its emerge cost and sacrifice a creature whose mana value is 3, Decimator of the Provinces’s mana value remains 10.

You may sacrifice a creature with a mana value of 0, such as a token creature that’s not a copy of another permanent, to cast a spell for its emerge cost. You’ll just pay the full emerge cost with no reduction.

An ability that triggers when a player casts a spell resolves before the spell that caused it to trigger. It resolves even if that spell is countered or otherwise leaves the stack without resolving.