Oathkeeper, Takeno's Daisho
Legendary Artifact — Equipment
Equipped creature gets +3/+1.
Whenever equipped creature dies, return that card to the battlefield under your control if it's a Samurai card.
When Oathkeeper is put into a graveyard from the battlefield, exile equipped creature.
Equip 
Arnie Swekel
Champions of Kamigawa (CHK)
• #265Rulings
Oathkeeper's second ability checks whether the card's creature type is Samurai, not whether the creature was a Samurai when it left the battlefield.
(wotc • 2004-12-01)
Rulings
Oathkeeper's second ability checks whether the card's creature type is Samurai, not whether the creature was a Samurai when it left the battlefield.
(wotc • 2004-12-01)