It needs five to survive using its ability, and doesn't have a built-in way to get more counters
It doesnt have its own showcase frame yet, and so March of the Machine is introducing it ahead of the full-scale return to that world later this year in Lost Caverns of Ixalan
Consider some of the vicious things you can run: Elspeth, Sun's Champion, Enter the Infinite, Omniscience, Darksteel Forge, or Dragonstorm
You can only use 1 effect of "Attribute Gathering" per turn, once per turn
Ashiok, Nightmare Muse Limiting Factors : Ashiok, Nightmare Muse is just a torchbearer for a whole class of planeswalkers that have big efficiency problems
Possibly the best of all these cards is Righteous Valkyrie