The Magician Lord achievement is earned by completing the 3 Mausoleums found throughout all 3 of the Cuphead worlds. These will require you to master the parry ability and use speed to defeat the ghost that are trying to reach the urn in the middle of the room.
The first room will introduce you to simple ghost which will just fly towards the urn. They will get faster towards the end of the level so keep that in mind.
The second room will introduce you to a Pac-Man like ghost that will fly around in a circle as it closes in on the urn. This will require you to hit it either as its in the air or next to the urn while defeating the ghost from room one.
The final room will introduce bigger ghost which when defeated will turn into two smaller ghost from room one. You must defeat all 3 types of ghost as the speed increases. You can also unlock the Bouncing Ball achievement
Here's a video showing the rooms