‘Living weapon’ is a keyword ability that appears on five artifact equipment cards in Scars of Mirrodin. In most cases equipment enters play and then must be attached to a creature you control. However living weapon equipment has a built in creature that will be put into the battlefield with the equipment attached via the living weapon triggered ability.

It works like this; when the equipment enters the battlefield the living weapon ability will trigger. When this trigger resolves a 0/0 Germ token creature will be put into play and the equipment will be attached to it. There are a few rules issues to keep in mind about this ability. First of all, state-based actions are not applied in-between when this creature enters the battlefield and when the equipment is attached to it. The Germ enters the battlefield and the equipment becomes attached all during the resolution of the triggered ability.

While it isn’t much of a creature, this 0/0 will trigger all relevant abilities that trigger when a creature enters the battlefield.

If the equipment is removed from the creature (by being destroyed, returned to its owner’s hand etc.) the Germ token creature will go to the graveyard when state-based actions are checked.

If the equipment leaves the battlefield before the living weapon triggered ability resolves, then the Germ token will still enter play, but as the equipment is not there to attach to it, the token will go to the graveyard right away.