Serperannus is a jungle snake with 10,000 HP (16,000 in Expert mode). She is summoned with Jungle Grub in the Underground Jungle. She behaves very similarly to other worms, burrowing through blocks and trying to hit the player once they turn around. However, after losing some health, she will send in 2 Exile's Underlings after the player and she becomes invincible until they die.
Torva-mes, The Grim Reaper is a grim reaper with 2,950 HP (4,720 in Expert mode). It is summoned using a Cursed Rune in The Underworld. It indefinitely floats towards the player alongside his minion scythe. When Torva-Mes gets too close to the player, it will dash at incredible speed, making it difficult to dodge.
Viyilblud is the core of evil with 4,000 HP (5,450 in Expert mode, and 8,000 in Nightmare mode). He is summoned using a Corrupted Shard in the world's evil. He follows a strange movement and attack pattern and does not allow the player to flee. When the player teleports too far away from Viyilblud, such as by using a Magic Mirror or a Rod of Discord, he will teleport with them.
If Viyilblud is lured outside the world's evil, he will enrage and become invulnerable to all damage.
Possessor is the purgatory incarnate with 3,000 HP (4,800 in Expert mode, and 10,204 in Nightmare mode). He is summoned with a Warphole Ring at night. He chases down the player throughout the fight while shooting Spirit Flames and Demon Scythes. He occasionally stops to fire a ring of ghastly projectiles.
If Possessor is not beaten by dawn, he will speed up to an incredible speed and instantly kill all players in the vicinity on contact.
Arlenon is the ruler of the sky with 30,000 HP (42,700 in Expert mode, and 70,800 in Nightmare mode). She is summoned with a Pearl of the Sky on a Floating Island. Arlenon acts in a way similar to Ice Queen, but instead of firing ice waves, she shoots Eye Beams. Just like the Ice Queen, her speed and attack rate increase as she loses HP. She also summons in Skyeyes.
Athazel is a devil with 28,500 HP (32,900 in Expert mode, and 50,500 in Nightmare mode). She is summoned with a Trident of Doom in The Underworld. Athazel, just like Torva-mes, has her own unique behavior.
Shift, Defender of Space is a member of Crystal Conflict's army with ??? health (??? in Expert Mode). He is summoned with the Forbidden Gem anywhere at night. He mainly attacks by hovering towards the player, shooting projectiles, and sending his head and arms after the player.
Polypus, The Great Oceanic Beast is a large octopus with 33,500 HP (53,600 in Expert mode). She is summoned with a Contaminated Rotten Shrimp in the Sunken Isles. Polypus slowly chases after the player, shooting projectiles and summoning minions to help her.
Post Moon Lord Bosses
These bosses can only be fought after defeating the Moon Lord for the first time within any given world. These bosses are the most difficult, and should be planned carefully before taking them on.
Oculus is an amalgamation of the Mechanical Bosses with 190,000 HP (294,500 HP in Expert Mode). It is summoned with the Mechanical Eye MK2 at night. It alternates between 4 AI patterns, all with different behaviors.
The Annihilation is a giant worm lurking in the Great Darkness with 100,000 HP (160,000 in Expert mode). He is summoned with a Pitch Blackness in The Great Darkness. He moves at an incredible speed and instantly kills all players upon contact with his head (In Nightmare Mode only).
Frezyn, The Ancient Ice Dragon is an ancient ice dragon with 400,000 HP (600,000 in Expert mode and 1,000,000 in Nightmare Mode). He is summoned with the Seal of Dragons in the Snow biome. He behaves like a Wyvern but uses an ice breath attack in front of himself.
Mortalos is the last sinner in Hell with 134,800 HP (188,720 in Expert mode). He is summoned with the Seal of Demons in The Underworld. He is considered one of, if not the most difficult boss in the Jetshift Mod. He constantly follows the player while slamming down his fists and shooting long streams of fireballs. He is the only boss in the mod that requires a certain platform to be built before he can be fought.
If the player attempts to escape the fight with Mortalos by escaping the Underworld, his watchdog will swoop in and kill the player in an (almost) undodgable dash.