Gjallar

When Gjallar enters the battle field you may
make one of your creatures unblockable until
end of turn
{t}: {p/c}{w}{w}{1} sacrifice Gjallar and either destroy
all creatures, enchantments and artifacts, or land.
This can be triggered at any time
Gjallar is the horn of Heimdallr, who watches for
Ragnarok and keeps safe the Bifrost, its sound can be
heard throughout the nine worlds as a warning of the
end of time