The Mario Spirit enemy is a boss in Area 6 and Area 8. It bears a good likeness of Mario, but is only a shadow of the actual hero.
Before Area 1Edit
Before the game starts, as Luigi and Mario walks through Boo Woods, if the player looks off to the left, if he or she looks closely, they can see the Mario Spirit staring at them.
During Area 6, when Luigi manages to capture the first portait ghost, the Mario Spirit begins running around the Dark Rooms that Luigi is in.
When Luigi makes it to the area where he faces the Mario Spirit, the enemy begins to manifest itself, much like a real ghost in the real world.
When Luigi defeats the Mario Spirit, he doesn't capture it because it escapes right at the last second.
In Area 8, when Luigi finds the Mario Spirit again, he begins battle with it on the roof.
When Luigi defeats the Mario Spirit, he captures it this time. If the player listens carefully as Luigi sucks up the Mario Spirit, he/she can hear it laugh.
The Mario Spirit bears a good likeness of Shadow Mario from Super Mario Sunshine.
In the events before Area 1, the part where the Mario Spirit is staring at Mario and Luigi is a reference to Super Mario Sunshine when the plane the heroes, Toadsworth and the princess was on crashed on the Delfino Airstrip.
The part where the Mario Spirit begins running around in Area 6 after Luigi captures the first portait ghost is also a reference to Super Mario Sunshine.
The laugh the Mario Spirit makes while being captured has the same tone as the voice Shadow Mario had in Super Mario Sunshine.