You can get a green cloak by doing tasks, which are the tasks you took at Zombie College. Follow them. I attached a picture to all the tasks of Zombie Academy. Some NPC's are on the 6th-7th floor, that is, don't go directly to the 8th floor after killing the Giant Zombies and Hyderabad.

If you don't know how to watch the game, you can play more. There are many posts there.