The Smoldergeist is the first official boss fought in Mario & Luigi: Dream Team. They are fought in a group of four under Pi'illo Castle. They are first seen where they put Mario and Luigi through different trials in order to pass. However, they then start to surround Princess Peach and Toadsworth getting trapped as Mario and Luigi passes by, they start to disappear. However, the Smoltergeists return with their fury burning as Mario and Luigi get their hands on Prince Dreambert's remains, a stone pillow in his image. The Bros. now have to fight them for their lives.
In battle, the Smoldergeists mainly attack by spitting fire at Mario and Luigi. When their flames are put out (such as from the beginning after Starlow puts them out), they will simply roll into either Mario or Luigi.
The Smoldergeists aren't difficult bosses as their attacks are simple to avoid. Mario and Luigi should only attack the ones without their flames on. Since they don't have Bros. Attacks or hammers at the time, Mario and Luigi must rely on jumping to defeat them. When they fire blow roll, make sure none of them hits you to tire them, putting their flames out, otherwise they'll stay strong and nothing changes yet.
- This is the only boss fight in Mario & Luigi: Dream Team where Starlow assists Mario and Luigi directly in battle.
- Smoldergeist's name is a reference to a Poltergeist, a name given to a type of ghost or spirit that causes disturbances.
- Additionally the boss's name sounds similar to Bouldergeist another boss in the Mario series.