Undead

Undead is a keyword ability. For the race Undead, click here.

If this card dies, return it to a battlefield you control during your next turn and change it's race to "Undead". If this card dies while it is Undead (meaning while it's race is Undead), it cannot return to the battlefield with Undead.

Rulings
While uncommon, a card may have both regen and undead, most likely through the effect of another card. If this is the case, the player may choose which effect activates at the time to card returns to the field. If a card is undead, and it dies, the player may use regen to return it to the field, but it becomes the type it was before it became undead, and must die again before it can become Undead.

A card with undead is not required to be killed in combat in order to return to the field. However if the card was killed because it's minimum defense became zero permanently, it cannot be returned with the effect of Undead.