The Blue Spook is the one of the most common enemies in the game, along side Revenants. A Blue Spook can be seen on the title screen of the game, as it glides around and interacts with the 'screen'.
The Blue Spook takes the general appearance of many modern depictions of ghosts. They are blue, translucent humanoid torsos, with skeletal arms and exposed ribs, with a vague skull-like head and a leering grin and hollow eyes. They lack a lower half of their bodies and glide around, leaving a transparent blue trail of ectoplasm in the air behind them.
Blue Spooks will sometimes take appearances of living humans in order to allude their victims (they take the form of students/teachers in Montsaye and scientist in the Military Base), which would most likely be their real forms from when they were living
Blue Spooks appear as vengeful, airborne spirits. They use two methods of attacking Lazarus. The first is their projectile attack, in which they fire a glowing, translucent orb of ectoplasm from their mouths. This delves minimal damage when compared to it's other form of attacking. The second attack could be considered it's 'rush' attack. The Blue Spook will change it's form and become a glowing shape in the vague form of a crucifix, and glide down towards the player in an attempt to 'pass through' them. This will result in a significant amount of health loss, as well as a visual distortion for the player which will wear off in a matter of seconds, but could leave the player visually impaired and vulnerable to other attacks. This attack, however, is easy to determine and will take a few seconds before the Spook charges the player, making it quite easy to dodge in time.
Occasionally during the Swamp level, Spooks can be summoned by an alerted Howler, and will awaken from the graves once a Howler has dug them up.
-Though having the appearance of many ghosts in modern media, the main inspiration for the look of the Blue Spook could have possibly come from the librarian ghost in the film, Ghostbusters.
-Another similar looking design could be seen from the Wraith from the 2012 satirical horror film, Cabin In The Woods.