Feroz's Ban is a card that has always frustrated me because it's an interesting sphere effect that would be perfectly at home in shops if it weren't so overcosted. It's also hard to fix this by just reducing the CMC because it quickly becomes OP so I was thinking about what it would take to make this vintage playable without being overly oppressive. This is what I came up with:
Mishra's Ban

Legendary Artifact
Creature spells cost

more to cast.
I think making it legendary balances it by not allowing multiples to stack and it also makes a lot of sense with the flavor of the original card. I think reducing the cost to by two makes it playable without being undercosted. So would this be playable and balanced?