Toaster

Toaster is (technically) the 15th difficulty in the difficulty chart. It is the same as Why in JToH and RoorXD in JHT. It is made to signify in curator reviews that a tower/citadel/whatever is impossible because of at least one jump. If you really want to count it, there is 1 Mini Tower with this difficulty:

Whitelist:
Not Even a Tower Ultra

Trivia

 * The emote in the AHT wiki is the Object Shows' Toaster character having a weird face.

This is (technically) the final difficulty. There is nothing else for you.