The Morph mechanic originated in the Onslaught block, and was reintroduced in Time Spiral. The loser was based on the card (create), which has a similar effect. It creates an alternate method of bringing the creature into play, either making it cheaper than normal or giving extra benefits.
A card with the Morph mechanic may be played any time you could play a sorcery for 3 generic mana. When played this way, it comes in face-down and is treated as a totally bland 2/2 creature. It has no type, no color, no converted mana cost, no name, absolutely no status other than being a creature with 2 power and 2 toughness.
Morphing the Card
While it is face-down, you may play the card's morph cost anytime you could play an instant to turn it immediately face-up. This action does not use the stack, so it may not be responded to. However, many morphing creatures have abilities that trigger when they turn face-up, and those abilities are put on the stack to be responded to. For example, (create)'s effect destroys an artifact or enchantment when it's turned face-up (similar to Naturalize from the same set). While there's nothing you can do about him turning face-up, you can respond to the triggered ability by somehow protecting the targeted card or countering the effect.
When turned face-up, the card is not treated as an entirely new card, so it is not affected by Summoning Sickness simply due to turning up.
The ability to conceal exactly what creature you're playing, reduce its cost, and/or have a "spell on a stick" has many very useful applications.
- A creature which would otherwise be unable to attack can at least attack once if it attacked while face-down. Take (create) for example. It normally can't attack the opponent unless he controls an Island, a restriction that usually means it won't be able to attack. However, if you attack while it's face-down and then morph it face-up during combat, it will still be attacking at its full force. This kind of tactic is typically more useful in Limited play, though.
- Some creatures with Morph have triggered abilities that occur when they damage the opponent. You can choose to turn it up after your opponent has declared it to be unblocked and get that effect in there as a surprise, similar in nature to Ninjutsu. Naturally, this will usually work only once per creature at best.
- Though it will take up multiple turns, you can get a strong creature out significantly earlier than you normally could and effectively give it Haste. Grinning Demon is a perfect example of this, because while the morph cost is identical to its regular mana cost, you can get it to hit on turn 4 via morphing.
- In Limited play, morphing can help you focus your mana curve, even if you're not playing the card's color at all. It's entirely legal, though not exactly effective, to play an off-color morph card in your deck as a colorless Gray Ogre. It also means that if you are playing that card's color, but you haven't drawn the colors you need to play it naturally, morphing it will still let you have it as some kind of creature while you gather the right mana you need to flip it up.
- Because morphing does not use the stack, you can respond to abilities with Split Second. An example of this is with a face down Willbender you can redirect the target of an Extirpate or (create).