Necron Tombworld

Necron Tombworld enters the battlefield tapped.
{t}: Add {c}.
{2}{t}, Exile a creature card from your graveyard:
Create a 2/2 Black Necron artifact creature token.
If the exiled card has the artifact subtype, create a
4/4 colorless Construct artifact creature token
instead.
"Awaken, ancient sentinels, and guard our slumber for eternity."