Drownyard Behemoth

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.”

The mana value of the back face of a double-faced card is the mana value of its front face. The mana value of a melded permanent is the sum of the mana values of its front faces. A creature that’s a copy of either has a mana value of 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.

A creature’s mana value is determined solely by the mana symbols printed in its upper right corner (unless that creature is the back face of a double-faced card, is a melded permanent, or is copying something else; see below). If the mana cost includes {X}, X is 0. If it’s a single-faced card with no mana symbols in its upper right corner (because it’s an animated land, for example), its mana value is 0. Ignore any alternative costs or additional costs (such as kicker) that were paid as the creature was cast.

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

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.

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.

There is no moment during the turn Drownyard Behemoth enters the battlefield in which it doesn't have hexproof. The earliest opportunity for an opponent to target it is during the next turn's upkeep step.