A Boss Monster is normally an NPC found rarely in Terraria that is much harder to kill than other monsters. It generally has much stronger attacks than a normal enemy, more defense, and considerably higher HP. In addition most boss monsters have their own AI, allowing them set movements to go by.

Many bosses can be summoned by an item like the Suspicious Looking Eye or Worm Food. These are the most widely known of the bosses throughout Terraria:

• King Slime (Mini-boss)
• Eye of Cthulhu
• Eater Of Worlds
• Skeletron
• Wall of Flesh
• Wyvern (Mini-boss)
• The Twins
• The Destroyer
• Skeletron Prime
• Ocram (Xbox and PS3 only)

Pre-Hardmode

Eye of Cthulhu

Main article: Eye of Cthulhu

The Eye of Cthulhu (commonly referred to as The Eye) is usually the first boss players will encounter, this is due to the fact that The Eye is considered the easiest pre-hardmode boss. The Eye comes in two forms. The first form has 15 attack, while the second form has 23 attack. The Eye of Cthulhu can be summoned by using a Suspicious Looking Eye (which can either be found in random chests or can be crafted from 6 Lenses at a Demon Altar) at night. The Eye can also spawn itself if certain criteria are met. While playing, the player may get the message, "You feel an evil presence watching you...", which means that the Eye will awaken soon. After a few minutes the message "The Eye of Cthulhu has awoken!" will appear and the boss will promptly start to attack the player. You can summon The Eye anywhere, as long as it is night. Sometimes when you are under ground and you see "You feel an evil presence watching you...", and you die it will spawn after you respawn so you get killed twice in the period of 5 minutes.

Eater of Worlds

Main article: Eater of Worlds

Eater of Worlds is a worm-type boss monster. He can be summoned in the corruption by smashing three shadow orbs and he can also be summoned with Worm Food, which can be crafted at a Demon Altar - however, it can only be summoned in The Corruption.

The Eater of Worlds has 53 parts in three segments; head, body and tail. To beat this boss all segments must be slain. If the head is destroyed, the next body segment will automatically take its place as a head. The same happens with the tail. If you destroy a body segment, he will split into two separate worms. Overall, if you avoid the head's massive attack of 40, the boss is fairly easy to defeat, especially with weapons that deal damage multiple times per strike, such as Vilethorn.

It is the only boss that can drop Shadow Scales, which are needed to forge Shadow Armor.

Skeletron

Main article: Skeletron

Skeletron is a boss which can only be defeated once per world and has no summoning item. He can only be summoned by talking to the Old Man in front of the dungeon at night and choosing the option "Curse". It is advised to be prepared because after that he will transform into Skeletron and attack you. His hands each have 800 and his head has 4400 . His hands do 30 damage if they touch you and his head will do a spin attack that does 35 damage. Be quick to defeat this boss and summon him at the very beginning of night because once dawn comes Skeletron will hit you for 9999 damage, resulting in instant death. If you die before defeating Skeletron, you will not be able to fight him again until the next night, when the Old Man will respawn.

After defeating Skeletron, the player will gain access to the Dungeon.

Hardmode

The Twins

Main article: The Twins

The Twins are the hardmode counterpart to the Eye of Cthulhu, except there's two of them; and are both connected together as seen in the photo.

The Twins, namely Retinazer and Spazmatism, are bosses summoned with the item "Mechanical Eye", which is crafted at a Mythril Anvil after summoning and killing the Wall of Flesh. In order to make a Mythril Anvil, one must kill the Wall of Flesh, use the Pwnhammer and break Demon Alters and "Bless your world" with Cobalt, Mythril, and Adamantite.

They have similar attack patterns to The Eye of Cthulhu, but their second forms use laser and demon fire attacks respectively. The two both need to be defeated to count as a boss kill.

The Destroyer

Main article: The Destroyer

The Destroyer is a worm type boss monster. He is the Hardmode counterpart of the Eater of Worlds. However, unlike the Eater of Worlds, it does not split into parts.

The Destroyer is summoned with the item "Mechanical Worm", which is crafted at a Mythril Anvil after summoning and defeating the Wall of Flesh.

The Destroyer drops 15-30 Souls of Might and 5-15 Greater Healing Potions. Souls of Might are required to make many Hardmode weapons and tools, like the Excalibur and Megashark. Getting the souls can sometimes be a problem, as if the Destroyer is defeated while mostly underground the Souls of Might may be dropped on top of blocks.

Skeletron Prime

Main article: Skeletron Prime

Skeletron Prime is the Hardmode counterpart of Skeletron. Similar to The Destroyer, he is also made of metal.

Skeletron Prime is summoned with the item "Mechanical Skull", which is crafted at a Mythril Anvil after summoning and defeating the Wall of Flesh.

Skeletron Prime drops 20-30 Souls of Fright and 5-15 Greater Healing Potions. Souls of Fright required to make many Hardmode weapons and tools.

Mini-bosses

King Slime

Main article: King Slime

The King Slime, as one might gather, is a slime. It is blue in color and enormous, roughly 10 blocks wide and 5 blocks high. It will decrease in size and spawn blue slimes when it takes damage. It appears to have a Ninja trapped inside it.

King Slime is summoned with the item Slime Crown, crafted with a Gold Crown and 99 gel at a Demon Altar. There has been a bug associated with the King Slime, sometimes causing the boss to not spawn/appear. This may be due to the fact that he spawned inside a cave and cannot get out.

The King Slime actually drops a little amount of Gel when he dies, and all of the blue slimes spawned when the King Slime is attacked also drop gel. The King Slime also drops gold coins, a piece of the Ninja Set and some lesser healing potions.

The King Slime is the biggest slime in the game so far.

Wyvern

Main article: Wyvern

The Wyvern is a large Hardmode Mini-Boss. It is a large, curling, dragon-like creature that attacks at high speed.

Wyvern is not summoned - it occasionally spawns in the sky, around the same point that Harpies spawn. It spawns without warning, so the player should be careful when they are at a high elevation in Hardmode.

The Wyvern Drops 5-13 Souls of Flight and 1 gold coin.

Notes

To balance out the need of the three Weapon types (Melee, Ranged, Magic), the three Hardmode bosses can be each killed best with a diffrent type: Skeletron Prime is easiest to kill with magic, The Destroyer with melee, and The Twins with ranged.