Altar of the Wretched // Wretched Bonemass

Craft usually asks you to trade a card's front face for a bigger, weirder back face and to pay for the swap in mana plus material. Here the material is creatures, and the back face inherits them wholesale. Wretched Bonemass has no fixed body: its power and toughness are the summed power of everything exiled to craft it, and it absorbs every relevant keyword those creatures carried. Feed it something with flying, deathtouch, and trample and the Skeleton Horror walks away with all three. That is the design hook. The front side is a sacrifice-for-cards altar, and the crafted back side is a keyword scavenger that reassembles the parts you fed it into a single evasive threat whose size scales with what you gave up.

The front half is unabashed card advantage: sacrifice a nontoken creature with power X and you draw X while milling X, netting the full X cards in hand with your graveyard padded as a side effect. That mill is fuel, not a cost, and it points squarely at the craft cost, which exiles creatures from the graveyard to assemble the back face. The altar dumps bodies into the yard; the craft ability spends them to build the Bonemass. The recursion clause is a separate insurance policy, buying the artifact back to hand for if it dies before you commit. All three modes point the same way: they reward a board full of expendable creatures, and they reward you for having scattered the right keywords across it. This is a two-stage engine dressed as one card, built for tables that treat creatures as parts rather than presence.