would this character be possible?

alright so back on another site, i had a character named "boo". he was a ghost that everyone could see, but he had no real shape. he was just a blob spirit that would change into the shape of people and become the colour of their aura. all he knew how to say said was "boo".
his general shape was like,,,
[spoiler][/spoiler]
and i do believe he had the ability to possess npc that i controlled, so he definitely isn't invincible if it comes to battle, as i always put him into a body for that and if that body was destroyed, he was out of that battle.