The Collector/5 BSC

The Collector is the final boss in Dead Cells. He was added in v1.2, aka the Rise of the Giant DLC. He can only be reached on 5 BSC difficulty in the Observatory.

Moveset
The Collector changes phases over the course of the fight. His two main phases use a different set of attacks. After taking enough damage, he will go invincible and teleport you and himself to a different room.

The phases typically go in the following order:

Melee -> Interim -> Ranged -> Melee -> Interim -> Ranged -> Melee -> Final

It is possible to skip some phases depending on how much damage you deal to him.

Drink Potion
When the Collector's HP gets low (about 1/2), he will drink from the panacea, healing him back to full health. If his HP drops below ~40% he will stun everything around him and gain a force field, which goes away after he restores his health.

After the third time he drinks the potion, he will immediately transition to his final phase.

Melee Phase
The Collector uses the following attacks:

The second time you get sent to this room, the Collector spawn a spike ball that bounces around the arena. The third time, there will be two spike balls.

Ranged Phase
In this phase the Collector will use a different set of attacks:

The second time you are sent to this room, the walls in the arena will be covered by damaging enemy columns.

Interim Phase
The player will be teleported to a room with three doors which will open and let a few enemies loose. During this phase some bombs will fall from above. This phase is the safest one by far.

The first time, he summons three early game enemies, and the second time he summons two mid game enemies.

Once all the enemies are defeated, he will teleport back to the arena and leave himself vulnerable for a few seconds. Afterwards, he will go invincible and teleport the player to a different room again.

Final phase
The player will be teleported into a room with a giant telescope. Here, the Collector will use his full moveset. The Collector takes less damage than in the other phases.

At ~80% HP, the Collector will drink his potion. However, he will not be invincible while drinking it this time. When you hit him while he's drinking it, it will knock the potion out of his hand. Grab the potion and drink your flask to gain a massive boost to damage and damage reduction. You must do this to kill the Collector for good.

General

 * Crusher is highly effective against the Collector. It will slow him down greatly and will constantly interrupt some of his attacks like his tornado attack.

Attacks

 * Try to attack in the air during his melee phase, that way, it'll give you some time to avoid his ground slam attack.
 * The safest way to dodge his syringe lunge attack is to cling onto the wall. It's also the best way to dodge both the ground slam and the bombs. Avoid doing this in the final phase, though.
 * For his spin attack, if you are cornered, roll towards the wall before he is about to hit you.
 * To dodge through his double tornado attack, roll through each column, then jump away and repeat.
 * Parrying the tornadoes is a valid option, but you will need some distance from the wall, especially if it's surrounded by energy. Even without it, he can start using his beam attack right after and hit you with the spikes. Hold in the direction towards the Collector to minimize the distance knocked back.
 * His orb attacks have consistent timing, the only thing that could throw it off is your distance.
 * His beam attack comes out fast and have a set attack time period, even when he starts doing it from far away. Focus completely on dodging this move, you won't usually be able to hit him while he's above you anyway.
 * For the beam attack, the visual cue is very subtle. Listen for the audio cue to help make it easier to time your dodge right.

Lore
When the Beheaded reaches this biome, the Collector reveals his plans to create the panacea, a fabled cure to all diseases, using all the cells collected by the Beheaded, further implying his true identity as the Alchemist. He asks the Beheaded to deposit them in the Catalyst next to him. Although the Collector doesn't believe the legends passed down by the first Alchemists of the island, he attempts this experiment in a last-ditch effort to cure the Malaise and save the island as well as himself. It turns out the remedy works, but it drives him mad with power. Thus, the Collector tells the Beheaded to go back and gather more cells, which triggers the fight.

During the fight, which consists of a number of phases in different rooms, the Collector keeps healing by drinking the Panacea. Once the player has dealt enough damage to the boss and/or survived through all phases, the Collector teleports himself and the Beheaded in the last room. Then, he becomes vulnerable when he attempts to drink, and drops the Panacea when hit. The player can then pick up the Panacea, which fills their potion slot with a blue liquid. If the player drinks it, their attacks will become extremely powerful and quickly defeat the boss.. As he was dying, the Collector exclaims that what he was doing ruined the island, and he was trying to revert his consequences. The Beheaded ends the Collector by stomping his face three times, exclaiming pity as he walks away. It is at this moment that he realizes that the cure is effective, and that he doomed the island's fate by killing the only person able to recreate it. Then, his body is vanquished by an unseen force, before he realized that his entity wasn't destroyed. He proceeds to crawl away in a scuffle as the credits roll.

Trivia

 * Due to a visual oversight, when the Beheaded kicks the Collector's corpse, the syringe somehow moves in sync.
 * Even when the player is not wearing the Classic Outfit, the cut-scene where the Collector is killed will not change. The only exception is the King Outfit.
 * When the Beheaded kicks the Collector's face, the game may play a rubber ducky sound.