The Last of Its Kind

The last of its kind It's a creature only if there are
no other creatures on the battlefield.
At the beginning of your upkeep, if it's not a
creature put one Doom Counter on it.
{t}, remove six Doom Counters, sacrifice this
artifact: Destroy all creatures on the battlefield.
—
The beat of his heart not only marks what is left of its
life, but that of everyone else.