Statue Armour Ghost
From the Super Mario Wiki
Greenies using statue armours are only fought and seen in Front-Door Key. Luigi encounters them in the Ceremonial Chamber, having to beat two of them to get through. In Stop the Knightmare, six suits of armor are possessed by the Tough Possessor.
To attack Luigi, the Statue Armour Ghosts charge at him fairly fast, then attack with their weapon, dealing 20 damage if successful. However, if they don't hit Luigi, the ghost will have to pull the weapon out of the ground, taking time to do so, this is when Luigi can reveal the ghost beneath the suit, by using his Poltergust 5000's Power Surge on the carpet it is standing on, making the knight fall which breaks its suit of armor, revealing the ghost. The fight after that is just sucking it up.