Geralf's Messenger and all the other Undying creatures
Sure in most cases you still need a sac outlet but there are enough cheap ones or ones which are resilient to removal themselves like Woe Strider or any of the many non creature sac outlets.
I think the deck user meant is the yawgmoth sacrifice decks where this would just slot in easily
And this is a deck /combo thats viable and proven to work as it 6-0 a modern challange last
It would still be a fine addition even without hexproof but hexproof might put it over the top