The value of X is calculated continuously as the number of creature cards in graveyards changes.

If lethal damage is dealt simultaneously to the equipped creature and another creature, both creatures are put into the graveyard at the same time. The equipped creature won't get an additional bonus from the other creature.

If there are no creature cards in any graveyard when Bonehoard's living weapon ability resolves, the Germ will be 0/0 and put into its owner's graveyard.

Although creature tokens go to the graveyard before ceasing to exist, they never count as creature cards and won't increase the bonus granted by Bonehoard, however briefly.

If the living weapon trigger causes two Germs to be created (due to an effect such as that of Doubling Season), the Equipment becomes attached to one of them. The other will be put into your graveyard and subsequently cease to exist, unless another effect raises its toughness above 0.

If the Germ token is destroyed, the Equipment remains on the battlefield as with any other Equipment.

The Germ token enters the battlefield as a 0/0 creature and the Equipment becomes attached to it before state-based actions would cause the token to die. Abilities that trigger as the token enters the battlefield see that a 0/0 creature entered the battlefield.

Like other Equipment, each Equipment with living weapon has an equip cost. You can pay this cost to attach an Equipment to another creature you control. Once the Germ token is no longer equipped, it will be put into your graveyard and subsequently cease to exist, unless another effect raises its toughness above 0.