This outclasses Boneyard and Graveyard in every way.
I would drop the cost of the unupped to 1
and make the ability free, without generating yards, but effecting Bone Walls.
The upped could generate two death effects every time, with a casting cost of 2
, but still a free ability.
I feel that removes the niche of the card, because it simply becomes another death effect generator. The idea was that you could run these in a deck WITH graveyards, to make mass skeleton production a viable tactic. You'd still need to have ways of playing / producing non-skeleton creatures in order to PRODUCE skeletons with this though, so it wouldn't be too OP.
Also, the only properly viable decks that use Graveyard are things like CCYB or similar mutation decks, and in those, splashing graveyard might still be a better option. No sacrifice needed, can start producing skeletons on the turn it is played. This, on the other hand is designed to make a whole range of skele-production decks faster.
Tbh, I just love Boneyard and Graveyard as concepts, and am just sad that they aren't really viable tactics. This aims to change that.
My fave idea is a time duo. This, some Bonewall, De-Vu, Eternity. To start with, eternity rewinds De-Vus that have already split, while Stone/Alter kills the other half. Onece the tactic progresses, you can start using Eternity on the Skeletons to give random creatures. The bad creatures can just be sacrificed because they are no longer Skeletons.