What is the following sentence an example of?
My sister's room is a pig pen.

Metaphor! It isn't using like or as!!!

Simile because it says my sisters room is a pig pen which is a simile

This is a metaphor, not a simile. Similes use "like" or "as" in the comparison, and since this statement reads, "My sister's room is a pig pen," which uses neither like nor as in the comparative statement, it isa metaphor.