Mamut, Only Survivor

Indestructible, Hexproof, Defender, Vigilance,
Trample.
When Mamut, Only Survivor enters battlefield, as
long as this creatur stays on the battlefield, Artur
can not change owners.
Second round {5}- You may cast this card from your graveyard for its flashback cost. Then exile it.
—
"There were only 1,000 of them, but then ... Arthur
came."