The card exiled with Ire Shaman's last ability is exiled face up.

Under normal circumstances, you can play a land card exiled with Ire Shaman only if you haven't played a land yet that turn.

Turning a face-down creature with megamorph face up and putting a +1/+1 counter on it is a special action. It doesn't use the stack and can't be responded to.

If you don't play the card, it will remain exiled.

If a face-down creature with megamorph is turned face up some other way (for example, if you manifest a card with megamorph and then pay its mana cost to turn it face up), you won't put a +1/+1 counter on it.

Megamorph is a variant of the morph ability. You can find more information on morph on cards with morph from the Khans of Tarkir set.

Playing the card exiled with Ire Shaman's last ability follows the normal rules for playing the card. You must pay its costs, and you must follow all applicable timing rules. For example, if the card is a creature card, you can cast that card only during your main phase while the stack is empty.

If a face-down Ire Shaman attacks and is blocked by one creature, turning it face up won't cause it to become unblocked.