Ghost Knight

The Ghost Knight is an optional enemy in Mother 3. It is found in a single room in Osohe Castle. He is disliked by all other ghosts. A ghost located in front of the Ghost Knight's room will ask the player to defeat him. He is actually a Ghost Armor, but if he is encountered in battle before fighting the other two enemies in the room, the Ghost Armor, Ghost Sword and Ghost Shield will combine into the Ghost Knight.

Battle Memory description
"Once the empty-handed armor gets a hold of its sword and shield... terrible things will happen."