Creatures with augment don’t have a mana cost and can’t be cast.

Augment is an activated ability that you activate from your hand. To do so, reveal the card, choose a target host creature, and pay the augment cost. As this ability resolves, if the card with augment is still in your hand, put it onto the battlefield combined with the host creature.

Augment can (and usually does) change the name, card types, subtypes, rules text, and power/toughness. The combined creature will have (at least) two artists and may now have multiple colors. Anything covered up in the augment process doesn’t count, so ignore things to the left of the “metal bar” in the art of host creatures.

Augment can’t target creatures that aren’t host creatures.

The creature card with augment isn’t put onto the battlefield until the ability resolves. This means if the host is destroyed, the creature with augment stays in your hand. You can’t choose a different host, but you can activate augment again if there’s another host available.

You can’t activate augment unless there is a host creature on the battlefield. It doesn’t need to be yours. Note though that if you augment another player’s host creature, they control the combined creature.

You can’t put more than one augment card on a single host creature. Once a host creature is augmented, the host part gets covered up and it’s no longer a host creature.

Monkey- : règles, fonctionnement et interactions (MTG)

Monkey- is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Whenever a nontoken creature you control dies, Augment (, Reveal this card from your hand: Combine it with target host. Augment only as a sorcery.)

How it works : Monkey-

Original English text — Wizards of the Coast / Scryfall

#1January 19, 2018· Wizards of the Coast
Creatures with augment don’t have a mana cost and can’t be cast.
No other card is named in this ruling.
#2January 19, 2018· Wizards of the Coast
Augment is an activated ability that you activate from your hand. To do so, reveal the card, choose a target host creature, and pay the augment cost. As this ability resolves, if the card with augment is still in your hand, put it onto the battlefield combined with the host creature.
No other card is named in this ruling.
#3January 19, 2018· Wizards of the Coast
Augment can (and usually does) change the name, card types, subtypes, rules text, and power/toughness. The combined creature will have (at least) two artists and may now have multiple colors. Anything covered up in the augment process doesn’t count, so ignore things to the left of the “metal bar” in the art of host creatures.
No other card is named in this ruling.
#4January 19, 2018· Wizards of the Coast
Augment can’t target creatures that aren’t host creatures.
No other card is named in this ruling.
#5January 19, 2018· Wizards of the Coast
The creature card with augment isn’t put onto the battlefield until the ability resolves. This means if the host is destroyed, the creature with augment stays in your hand. You can’t choose a different host, but you can activate augment again if there’s another host available.
No other card is named in this ruling.
#6January 19, 2018· Wizards of the Coast
You can’t activate augment unless there is a host creature on the battlefield. It doesn’t need to be yours. Note though that if you augment another player’s host creature, they control the combined creature.
No other card is named in this ruling.
#7January 19, 2018· Wizards of the Coast
You can’t put more than one augment card on a single host creature. Once a host creature is augmented, the host part gets covered up and it’s no longer a host creature.
No other card is named in this ruling.