The boss ghosts (called possessors) possess various things including; a giant spider, a staircase, a clock, some ice (turning it into an ice monster), and a giant set of armour.
Spiders appear as minor enemies throughout the game. The first mansion’s boss is a giant, possessed spider. Also a wave of spiders appear in the cutscene after beating said spider boss.
Several areas require you to use the 3DS’s gyroscope to navigate across beams. Luigi falls off if you mess up, but you don’t necessarily die unless you lose enough health.
At one point in a still picture, the main villain suddenly turns towards the player and laughs loudly. Some of the ghost enemies also jumpscare Luigi to distract him.