From the Super Mario Wiki
Sir Lance-A-Lots are robot enemies found in Wario: Master of Disguise. They first appear in the Smithsnorian Museum and are also seen in Sneezemore Cave, Sweatmore Peak, and the area leading up to Carpaccio's Lab. If they see Wario, they will charge at him with their lances. Their name is derived from Sir Lancelot, a legendary knight. Upon defeat, they are revealed to actually be disguised armadillos, which then run away.
This robot camouflages itself as a suit of armor and waits for unlucky passersby. Of course, the disguise only works if you usually keep armor around the house.