Tier 4 Upgrades are new options in The King of Towers Conception. Feel free to add anything you want!
Hoanganh13's Ideas (also Lantafik) Edit
Path 1: Make Knight into Templars. Costs 500 goods.
Path 2: Make Knight into Royal Knights. Costs 450 goods.
Path 1: Become Arena Masters. Costs 700 goods.
Path 2: Become Lord of War Minions.