Ultra Greed is fought in a unique vertical double-size room with golden Boss Room doors on all 4 walls in regular positions.
When Isaac enters the boss room, Ultra Greed starts out hanging on a noose before he abruptly cuts it off and lands on the ground. Ultra Greed cannot be damaged until he drops to the ground. Ultra Greed then performs a variety of attacks in addition to wandering around the room:
Stomps on the ground 4 times, spawning a Keeper with each stomp. Only 4 Keepers can be alive at once.
Charges at Isaac when he is in line of sight.
Shoots either 3-5 coin projectiles in a spread from his mouth, or a cluster of coin projectiles, similar to Monstro.
Ultra Greed does not perform this attack if Isaac is far enough away.
Spins around the room, firing coin projectiles in random directions.
If Isaac is too close to Ultra Greed he performs a spin, kicking Isaac away in the process.
Stops moving and rotates his eyes in a slot machine manner. If both eyes land on the same symbol he then spawns multiple Ultra Greed Coins of the same symbol.
If the two symbols on Ultra Greed's eyes don't match, he spawns blank Ultra Greed Coins (Spinner).
Spins on itself and heals Ultra Greed for 13.125 HP each if not destroyed.
If there are too many monsters/coins alive at once, Ultra Greed assumes a defensive stance. While blocking Ultra Greed takes much less damage from Isaac's attacks, and maintains this state until most of the monsters/coins have been killed.
All of Ultra Greed's attacks deal a full heart of damage and causes Isaac to drop coins on hit. If he walks over any coins on the ground, he collects them, healing him for 4.375 HP each.
When Ultra Greed has low health, he turns red, which increases his attack speed and movement speed. This effect also occurs if Ultra Greed is healed by enough Heart Ultra Greed Coins although only providing a temporary effect.
When Ultra Greed's health bar is depleted, he turns into a golden statue and drop the end chest and the Greed Machine. If in Greedier Mode he instead begins his second phase.
Playing on Greedier Mode gives Ultra Greed a second phase where his gold statue form comes to life. This phase is known as Ultra Greedier, and is the final boss of Ending 19. Additionally, he performs several new attacks:
The coin projectiles that Ultra Greedier shoots from his first phase now explode upon contact.
Slams his fists into the ground, creating explosions where he slams and causing golden Brimstone lasers to fire from the golden Boss Room doors that surround the room.
They can either come out from one pair of doors at a time or from all of them at once.
Jumps into the air towards Isaac's position, dropping exploding coins down below while travelling. Upon landing, rock waves are sent in various directions.
Stomps on the ground four times, causing a slew of Bomb Coins to rain from the ceiling.
These coins can spawn coin pickups when they explode, providing both healing for Ultra Greedier and extra coins for Isaac.
After defeating Ultra Greedier, he explodes, dropping a coin pickup and turning the entire room into solid gold. It is at this point when the end chest and the Greed Machine spawn.
Ultra Greed in-game.
Ultra Greed hanging from the ceiling.
Ultra Greed's backside as seen during a spin attack.
Golden statue form of Ultra Greed.
Ultra Greedier in-game.
Beta Ultra Greed's appearance/spritesheets
More beta images of Ultra Greed.
The Ultra Greed mode unlock in Korean. Notably, Ultra Greed has a beard.
Damage scaling is a mechanic introduced in The Binding of Isaac: Afterbirth to provide a more challenging experience to the players, enabling some enemies to retaliate against high damage attacks by deploying an "armor" of sort to greatly reduce the amount of damage taken. Further details and an in-depth explanation may be found here.
Using Gnawed Leaf and any damage-dealing orbital, stand in front of Ultra Greed when he is charging. Ultra Greed attempts to charge into the wall but will get stuck on Isaac. Waiting in this position will eventually kill him.
After Key Coins appear, using A Card Against Humanity causes spawned Gapers to be stuck and, as long as they're alive, Ultra Greed will not attack.
Having E. Coli (and perhaps other contact-based collectibles) is a fast way of disabling the Bomb, Key, or Heart Coins because they don't do contact damage. However, unmarked coins do.
Mega Blast alone is able to kill Ultra Greedier if the entire duration of the blast hits him.
Except for direct contact and the Brimstone lasers, all of Ultra Greedier's attacks only do explosive damage. Therefore having Pyromaniac or Host Hat makes this phase of the fight much easier to survive.
If you manage to spawn a Sticky Nickel (possibly through a D20) Ultra Greed may station himself over it and no longer move around the arena.
If Isaac enters the trapdoor created by a Rune of Ehwaz on this floor, it starts over.
Ultra Greed can pick up coins even after being turned into a statue.
Ultra Greed is the second ultra deadly sin boss to appear in the game, behind Ultra Pride, but is the first to appear as a final boss.
Teleporting out of the boss room after defeating Ultra Greed will cause the statue to disappear.
The name "Ultra Greedier" comes from the bestiary.
In Greedier Mode, when Ultra Greed is defeated for the first time, he will stay as a gold statue for 10 seconds before he begins to break out and turn into Ultra Greedier. On future runs, he will begin to break out immediately instead.
If Ultra Greedier is spawned with the Debug Console into any room besides his normal room or Shops, the entire room will still be turned to gold when he dies. This is due a special shader that turns on in the room when he dies, so using effects like A Card Against Humanity or XVI - The Tower? will make the grid entities spawned look golden
Any poop spawned in the Ultra Greedier fight, destroyed or not, will respawn as Golden Poop when Ultra Greedier dies and turns the room into gold.
There is an unused form of Ultra Greed in the game's sprite sheets with a goatee style beard and a less fit body build. He was supposed to be a boss that represented Tyrone Rodriguez , similar to how Ultra Pride represents Edmund McMillen and Florian Himsl. This spritesheet can be found in the file folder "delirium forms".
The Korean version of the game still has some images with the beard used in the game.
If Ultra Greed is defeated at the bottom of the room, the ending chest will spawn incorrectly, causing it to be unreachable.
If Ultra Greed is hit by a Chaos Card after being turned into gold, his death animation will replay and cause a lot of gut splatter.
If the player dies and respawns outside of the room while Ultra Greed is rolling his eyes like a slot machine, the slot machine sound will play continuously until the game is paused.
If the player manages to constantly push back Ultra Greed while he charges so that he won't touch one of the walls, he will become stuck in his charge animation and won't do anything else until defeated. This can be easily done with Ocular Rift or Knockout Drops and a high amount of luck or tears.