For just two mana, you give a creature indestructible until end of turn, and whenever it's dealt damage, it bulks up with +1/+1 counters
On top of that, when you sacrifice it, you get tempted by the ring, making it an auto addition to decks that care about the mechanic, or just to at least make something harder to block
This is a returning mechanic, so you likely know how it works, but these cards offer some extra flexibility to considerlike if an effect lets you search your library for a bird, you could find Hakka, Whispering Raven but couldnt cast Alrund, god of the Cosmos
Third, these must be black-bordered cards
And so long as WotC keeps sticking to whatever design rules they adopted this year, well at least have one less balance headache to worry about in the future