Ultra War

Ultra War is a boss added in The Binding of Isaac: Repentance and is the third of the Ultra Harbingers fought before The Beast in Home.

Behavior

Phase 1

Ultra War charges in from the side of the screen and has two attacks which he alternates between:

Throws a large, Giga Bomb that deals contact-damage and explodes mid-air in a cross pattern that spreads across the entire screen, similar to Bomber Boy Bombs. The Bomb also releases a burst of 12 lines of 4 projectiles outward when it explodes. This attack is repeated 3 times.
Charges off-screen, then wraps around the bottom of the screen 3 times, creating 4 to 6 pillars of harmless light in alternating positions across the screen, from which large lava projectiles launch upwards with staggered timing.

Phase 2

Ultra War dismounts from his hobby-horse and has two new attacks which it alternates between:

Chases Isaac, then lunges diagonally downwards in Isaac's direction. After, Ultra War releases 4 streams of fire in the cardinal directions as well as a small burst of slower moving fires in all directions. This attack is repeated 2 times.
Lunges diagonally downwards while holding a large bomb which explodes in a cross pattern that spreads across the entire screen. Ultra War then bounces across the sides of the screen 3 times while moving upwards before plummeting into the lava below. When Ultra War emerges, he creates 4 to 6 large lava projectiles that launch upwards with staggered timing.

Upon death, Ultra War explodes, which can damage Isaac at close range.

Gallery

Ultra War tossing a bomb, first phase.
Ultra War in his second phase.
Ultra War bouncing around while holding a bomb, second phase.
Ultra War death portrait.
Concept sketches for Ultra War's behaviors.

Notes

If Isaac has the Safety Scissors, the Giga Bombs Ultra War throws will be defused and fail to explode, after which they can be picked up or left to fall into the lava.
Ultra War's Giga Bombs can be killed by Euthanasia shots.
The lava projectiles can be slowed and knocked down with certain slowing items such as Censer and high knockback tears.

Damage Scaling

Damage scaling is a mechanic introduced in The Binding of Isaac: Afterbirth to provide a more challenging experience to players, enabling some enemies to retaliate against high damage attacks by deploying an "armor" of a sort to greatly reduce the amount of damage taken. Further details and an in-depth explanation may be found here.