Eldrazi Devastator -> Roving Keep (cheaper, but otherwise downgrade)
Pierce Strider -> Bottle Golems (lose life/gain life)
Carnivorous Death-Parrot -> Foul Watcher (similar enuogh)
Eldrazi Skyspawner -> Moonfolks Puzzlemaker
Man-o'-War -> Frost Trickster (bounce -> hard tap) (I guess it's fine to have two of these while I'm working on the cube)
Mistral Singer -> Aven Wind Mage (basically the same thing)
Pierce Strider -> Bottle Golems (lose life/gain life)
Carnivorous Death-Parrot -> Foul Watcher (similar enuogh)
Eldrazi Skyspawner -> Moonfolks Puzzlemaker
Man-o'-War -> Frost Trickster (bounce -> hard tap) (I guess it's fine to have two of these while I'm working on the cube)
Mistral Singer -> Aven Wind Mage (basically the same thing)
Gurmag Angler -> Terrus Wurm
Aether Chaser -> Zada's Commando (loses energy counter thing)
Burning Prophet -> Fire Urchin (loses scry thing)