Rattleclaw Mystic

Morph lets you cast a card face down by paying 3 generic mana , and lets you turn the face-down permanent face up any time you have priority by paying its morph cost.

Although turning a face-down creature with morph face up doesn't use the stack, Rattleclaw Mystic's triggered ability does use the stack, and players can respond to that ability. Notably, you can't turn Rattleclaw Mystic face up while casting a spell or activating an ability. You'll need to turn Rattleclaw Mystic face up and have its triggered ability resolve before you can spend that mana.

When the spell resolves, it enters the battlefield as a 2/2 creature with no name, mana cost, creature types, or abilities. It's colorless and has a mana value of 0. Other effects that apply to the creature can still grant it any of these characteristics.