Lol

Someone who lives in a pineapple under the sea.

A mugger who steals mugs

Someone who tests the breakability of mugs.

A person with a mug stuck in his head

A tree

A mug used in a jungle

Muggle? Don’t you mean muffin?

An underrated person (wait that's true lmfao)

So for the wrong answer:

A wizard of the highest degree is called a Muggle(meh I am bad at this)

A wise old man who invented guns.