Flies high into the air and then slams down on Isaac's location when she started the attack, releasing short-ranged rock waves, 8 curving blood projectiles, and 16 regular blood projectiles, all in a ring.
The rock waves from this attack can kill the bats spawned by her.
Screeches and starts charging downward repeatedly, looping back to the top of the room above Isaac when she charges off-screen.
As she charges, she leaves a trail of blood projectiles which float in place for a short moment.
After she has charged 2-4 times, she screeches to a halt in the middle of the room and release a fast ring of 8 blood projectiles.
Battie will damage her summoned bats if she charges into them.
Notes
Using The Fiend Folio in Battie's boss fight will always create the friendly clone of Battie that will begin to attack the hostile Battie. When the friendly Battie does her slam, she will instantly kill the hostile Battie and cause her to drop the Baby Badge.
Champion Variants
Brown
Always spawns 2 Foamies instead of any other bats. Brown Battie cannot spawn more if 2 are alive, but can spawn 2 more if 1 is alive.
Foamies are also immune to Battie's attacks.
Her ground slam attack is quicker but no longer creates rock waves, only releasing 16 bone projectiles and 8 curving blood projectiles.
When she charges across the screen, she can come from any side of the room instead of only from the top.
For the next 3-4 dashes, she will alternate between vertical dashes, that can come from both top and bottom, and horizontal dashes, that can come from both left and right; these are always lined up with Isaacs position. she also leaves behind more projectiles in her wake.
Pink
Her ground slam releases a ring of rock waves and 8 homing projectiles.
When she charges across the screen, she alternates between charging downward and upward, and the projectiles she trails will split into 2 smaller ones horizontally with short range.
At the end of her charging attack, she releases 5 homing projectiles in a ring.
Video Showcase
Trivia
Delirium is able to transform into Battie, and has a unique coloration when doing so.
Battie originated from a planned sequel for the mod The Devil's Harvest known as "Deal of Demons", which was cancelled early in development.
Battie has been confirmed to not be a vampire.
Gallery
Battie Charging.
Battie after slamming the ground. (stupid)
Battie's appearance on defeat.
Delirium's appearance while transformed into Battie.
Drawing of Battie in the Bestiary and on Isaac's last will.
Caves.
Milk Tooths
One Tooths
Fat Bat
The Fiend Folio in Battie's boss fight will always create the friendly clone of Battie that will begin to attack the hostile Battie. When the friendly Battie does her slam, she will instantly kill the hostile Battie and cause her to drop the 
Baby Badge.
Foamies instead of any other bats. Brown Battie cannot spawn more if 2 are alive, but can spawn 2 more if 1 is alive.
Delirium is able to transform into Battie, and has a unique coloration when doing so.
Bosses 