Horde Ambusher

Morph is a static ability that functions in any zone from which you could play the card it’s on, and the morph effect works any time the card is face down. “Morph [cost]” means “You may cast this card as a 2/2 face-down creature with no text, no name, no subtypes, and no mana cost by paying {3} rather than paying its mana cost.” (See rule 708, “Face-Down Spells and Permanents.”)

Megamorph is a variant of the morph ability. “Megamorph [cost]” means “You may cast this card as a 2/2 face-down creature with no text, no name, no subtypes, and no mana cost by paying {3} rather than paying its mana cost” and “As this permanent is turned face up, put a +1/+1 counter on it if its megamorph cost was paid to turn it face up.” A megamorph cost is a morph cost.

To cast a card using its morph ability, turn it face down and announce that you’re using a morph ability. It becomes a 2/2 face-down creature card with no text, no name, no subtypes, and no mana cost. Any effects or prohibitions that would apply to casting a card with these characteristics (and not the face-up card’s characteristics) are applied to casting this card. These values are the copiable values of that object’s characteristics. (See rule 613, “Interaction of Continuous Effects,” and rule 707, “Copying Objects.”) Put it onto the stack (as a face-down spell with the same characteristics), and pay {3} rather than pay its mana cost. This follows the rules for paying alternative costs. You can use a morph ability to cast a card from any zone from which you could normally cast it. When the spell resolves, it enters the battlefield with the same characteristics the spell had. The morph effect applies to the face-down object wherever it is, and it ends when the permanent is turned face up.

You can’t normally cast a card face down. A morph ability allows you to do so.

Any time you have priority, you may turn a face-down permanent you control with a morph ability face up. This is a special action; it doesn’t use the stack (see rule 116). To do this, show all players what the permanent’s morph cost would be if it were face up, pay that cost, then turn the permanent face up. (If the permanent wouldn’t have a morph cost if it were face up, it can’t be turned face up this way.) The morph effect on it ends, and it regains its normal characteristics. Any abilities relating to the permanent entering the battlefield don’t trigger when it’s turned face up and don’t have any effect, because the permanent has already entered the battlefield.

If a permanent’s morph cost includes X, other abilities of that permanent may also refer to X. The value of X in those abilities is equal to the value of X chosen as the morph special action was taken.

See rule 708, “Face-Down Spells and Permanents,” for more information about how to cast cards with a morph ability.