Tsar
Tsar is a boss added in The Reheated Update that can be encountered in 
Dank Depths. He is a giant hulking mass of goop that uses gigantic pipes and grates in the arena to attack and to change his form at will.
Behavior
Tsar's arena will always spawn with at least 2 giant 
Grates on the ground in the left and right sections of the arena, as well as up to 4 Big Pipes in along the walls of the room. These will be used as apart of his attacks as well as in his "Grate Phase"
Tsar's behavior and attacks are dependent on his current form. He has 4 total: Dank (black), Septic (green), Pee (yellow), and Poop (brown).
- In his own boss rooms Tsar will always start off in his Dank form, but may appear as the other forms when encountered as a degraded boss.
- While idle, Tsar will slowly slide towards Isaac, and leave a trail of creep which reflects his current form:
- Dank Tsar leaves slowing black creep.
- Septic Tsar leaves damaging green creep.
- Pee Tsar leaves a thin trail of damaging yellow creep.
- Poop Tsar leaves slippery brown creep.
Tsar can periodically perform the following attacks:
- Coughs up a projectile volley slightly predicting Isaac's movement. This volley will leave creep as well as a few
Tar Bubbles.
- The type of creep left by this attack and by the spawned Tar Bubbles will match the creep that Tsar leaves will sliding.
- Tsar jumps into the air and slams down 3 times consecutively while continuing to chase Isaac.
- Tsar travels faster while in the air.
- When hitting the ground all Tar Bubbles in the room burst into projectile showers, and all Big Pipes within a short range will fire.
- Tsar navigates to the nearest grate and enters it, triggering the Grate Phase.
- If his health is below 20%, Tsar cannot perform this attack and will immediately cancel this phase.
Grate Phase
In this phase Tsar remains off-screen and can only be damaged when showing his face from beneath a grate or by attacking any summoned Tsarballs. He will repeatedly perform the following attacks until 5 Tsarballs have been summoned:
- Pokes his head up from a random grate and fires projectiles at Isaac.
- Dank Tsar fires a double layered spread of 7 projectiles.
- Septic Tsar fires a single large, slow, projectile that leaves a trail of damaging green creep.
- Pee Tsar fires a fast spread of 3 projectiles.
- Poop Tsar fires a random cluster of projectiles.
- Each time he pokes out his head, Tsar has a chance to change into a different form.
- A Tsarball erupts from a random grate alongside a radial projectile pattern.
- The type of Tsarball matches Tsar's last encountered form.
- Dank Tsar fires out a square pattern of 16 projectiles with the cardinal projectiles slightly offset outwards.
- Septic Tsar fires a ring of 6 projectiles that leave a trail of damaging green creep.
- Pee Tsar fires 8 fast projectiles outwards in a octagonal shape.
- Poop Tsar fires a volley of projectiles in random directions.
- A Big Pipe launches a Tsarball directly outwards until it hits a wall, alongside its usual attack.
- The Tsarball fired from a Big Pipe matches the type of pipe.
All Tsarballs will drift towards each other as they are spawned, joining together when close. Once 5 Tsarballs have been merged, or if Tsar falls below 20% health, they will reform into Tsar whose form matches that of the last Tsarball to be absorbed.
Spawns
Big Pipe
- Big Pipes are obstacles that appear exclusively in Tsar's Boss Room, and come in 4 types: Dank, Septic, Pee, and Poop. Their attack changes depending on their type.
- Dank Pipes launch a handful of
Blots. - Septic Pipes launch a short stream of damaging green creep that gets wider. The creep extends for about half the height of a normal room.
- Pee Pipes launch a thin stream of damaging yellow creep that extends across the entire room.
- Poop Pipes launch a disorganized volley of projectiles, as well as a large puddle of slippery brown creep near the pipe.
- Dank Pipes launch a handful of
- Big Pipes can only be activated to fire by Tsar's jumping attack, or as a part of Tsar's Grate Phase.
Tsarball
Tsarballs float slowly after Isaac unless there is a second Tsarball in the room. They can be attacked to deal damage to Tsar himself.
- If there is more than 1 Tsarball in the room they will instead float towards each other and merge.
- The resultant Tsarball will take on the type of the last merged Tsarball.
- Once 5 Tsarballs have merged into 1, or if Tsar falls below 20% health, the large Tsarball will reform into Tsar.
Video Showcase
Trivia
- Tsar's name is intended to be a pun on the words "tar" and "tsar".
- Tsar was a nobility title historically used by Eastern and Southern Slavic monarchs, meaning "emperor" or "king".
- Tsar, canonically, is the worst smelling boss in all of Fiend Folio lore, beating out
Cacamancer and 
Basco on the fact that Tsar not only is made of feces like them, but also tar, bile, and urine.
Gallery
Tsar's appearance while jumping.
Tsar peeking out from a grate in his "Grate Phase".
Tsar's appearance on death.
Septic Tsar.
Pee Tsar.
Poop Tsar.
Unique types of Tar Bubbles spawned by different Tsar forms.
Various types of Tsarballs.
Tsar's Big Grate.
Drawing of Tsar in the Bestiary and on Isaac's last will.
Tsar's various health bar icons if Enhanced Boss Bars is installed.
 Bosses 
| |
|---|---|
| Chapter 1 | Buck - Honeydrop - The Whispers - Griddle Horn - Buster - Meltdown |
| Chapter 1.5 | Ghostbuster - Cacamancer |
| Chapter 2 | Battie - Kingpin - Slinger - Monsoon - Aquagob |
| Chapter 3 | The Organization - Gutso the Great - Luncheon - Pollution - Tsar - Junkstrap |
| Chapter 3.5 | Warp Zone - Dusk - Madomme |
| Chapter 4 | Basco - The Sun - Peeping - Cacophobia |
| Chapter 4.5 | Mr. Dead |
| Minibosses | Psion - Gravedigger - Hermit |
| Vanilla Boss Champions | Golden Plum - Ghost Larry Jr. - Mucus Monstro - Technopin - Albino Widow - Beehive Fistula - Possessed Hollow - Wine Husk - Kidney of Infamy - Alien Loki - Fiend Mom - Alien Lokii - Grinch Krampus |