Guardian of the Forgotten

Because the permanent is on the battlefield both before and after it's turned face up, turning a permanent face up doesn't cause any enters-the-battlefield abilities to trigger.

To manifest a card, put it onto the battlefield face down. It becomes a 2/2 face-down creature card with no name, mana cost, or creature types. It's colorless and has a mana value of 0. Other effects that apply to the permanent can still grant it any characteristics it doesn't have or change the characteristics it does have.

Any time you have priority, you may turn a manifested creature face up by revealing that it's a creature card (ignoring any copy effects or type-changing effects that might be applying to it) and paying its mana cost. This is a special action. It doesn't use the stack and can't be responded to.