It consists of two enemies - one with 4 segments and one with 5; 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. Being hit by this variant of The Hollow will cause Isaac to drop coins.
Shoots a row of three bullets as an additional attack. Each segment spawns a Charger when destroyed.
This variant of the Hollow moves in a slightly altered pattern. It bounces off walls as usual, but also tries to chase Isaac by curving toward him. Each segment spawns a random amount of Attack Flies, Pooters or Fat Flies when destroyed. Much like Eternal Larry Jr, if its head is the only segment, it will move at 1/2 of its original speed and leave creep on its trail, though it will directly pursue Isaac rather than wandering around the room. It will not gain new segments.
Gray champion version of The Hollow.
Green champion version of The Hollow
Gold champion version of The Hollow.
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.
The Hollow has the most amount of Champion Variants out of any boss in the game.
In Rebirth, its head's HP has been reduced to the same as its body.