Queen Boo is the final boss of every (in other words, only) Luigi shame to date, although in Luigi's Bathroom
Kween buu

Queen Boo

she could only be defeated by hacking into the game and removing her although this is illegal (without hacking, the ending of the game would have Luigi dying, and Nintendon't confirms this is what the real ending should have been). After that she was replaced by that loser Waluigi as Luigi's arch enemy. Contrary to popular belief, she is not married to King Boo; the correlation is entirely coincidental. She's married to Waboo.