It consists of two enemies; each flies diagonally across the screen.
The movement of the boss resembles that of Fistula, though each segment can change the angle at which it bounces around the room, making dodging more difficult. The segments can be damaged and destroyed individually like with Larry Jr., which causes piercing tears to be very effective against him. If the room is filled with rocks, players may find themselves having a hard time dodging the Hollow, as the rocks will block player's movement (unless the player can fly), while the Hollow can fly over them.
Like with Larry Jr, each of the Hollow's segments are destroyed separately, therefore using The Necronomicon will instantly kill the Hollow.
The Hollow has a higher chance of appearing if you've killed Larry Jr before.
Each segment drops a coin when destroyed.
Each segment spawns a Boom Fly when destroyed.
Shoots a row of three bullets as an additional attack. Each segments spawns a Charger when destroyed.
- Sometimes, the green champion variant of The Hollow will use Larry Jr.'s head sprite when firing blood shots.
- Similarly, the green champion variant of Larry Jr. will use The Hollow's head sprite when firing blood shots.
- When the head of the Hollow spawns, the guts of a Host will be visible underneath, but will disappear after the smoke fades.
|Basement||Larry Jr. • Monstro • The Duke of Flies • Gemini • Steven • Famine|
|Cellar||Widow • Pin • The Duke of Flies • Famine • Gurdy Jr. • The Blighted Ovum|
|The Caves||Fistula • Peep • Gurdy • Chub • C.H.A.D. • Pestilence|
|Catacombs||The Husk • The Hollow • The Blighted Ovum • The Carrion Queen • Peep • Pestilence • The Wretched • Gurdy Jr.|
|The Depths||Loki • Monstro II • Gish • War • Mom|
|Necropolis||Mask of Infamy • Daddy Long Legs • The Carrion Queen • The Bloat • Loki • War • The Wretched • Mom|
|The Womb||Scolex • Blastocyst • The Bloat • Death • Conquest • Daddy Long Legs • Triachnid • Teratoma • Mom's Heart • It Lives|
|Utero||Teratoma • The Bloat • Death • Conquest • Daddy Long Legs • Triachnid • Lokii • Mom's Heart • It Lives|
|Sheol||The Fallen • Satan|
|First to fifth and seventh level||The Fallen • Headless Horseman|