Hone-onna

Lifelink, soulbond (You may pair this creature
with another unpaired creature when either enters.
They remain paired for as long as you control both
of them.)
When Hone-onna comes into play, search your library for a creature card, then shuffle and put
that card on top.

As long as as Hone-onna is paired with another creature, each of those creatures have undying.