Zhuge Bin, the Mindful

After a player has cast at least three instant or sorcery spells, if this creature isn't exemplar, it becomes exemplar. (To make a creature exemplar, double its base power and toughness. Exemplar creatures have protection from enchantments.)
As long as Zhuge Bin is exemplar, each opponent can cast spells only any time they
could cast a sorcery.