An example of an event. In this case, it is the Frost Legion.
The progress bar's range; on the left is the house and the right the limit, on a small world.
Events (also known as Invasions) are temporary occasions where varieties of special enemies spawn, most at elevated spawn rates, even near NPCs, and attack players. Some events can occur randomly during gameplay, while others can be triggered via certain summoning items or special circumstances. Events spawn their own unique enemies not seen during ordinary gameplay, which can, in turn, drop unique items that are only obtainable within the event. Some events also bring unique visuals and a unique atmosphere, such as an altered Moon and noticeable shaders applied to the screen. Events also are accompanied by their own special music, adding on to their theme. Depending on the particular event, they may last until a certain time limit is reached, or until a certain number of enemies are defeated.
On the 
PC version, 
Console version, 
Mobile version, 
Old Chinese version, 
tModLoader version, and 
tModLoader 1.3-Legacy version, a progress bar can be seen in the bottom right corner of the screen to indicate how far the player has gone into the event, and how far they are from completing it. It only appears during invasion-style events (Goblin Army, Slime Rain (only if 75/150 slimes are defeated), Old One's Army, Frost Legion, Pirate Invasion, Pumpkin Moon, Frost Moon, Martian Madness, and Lunar Events) and will not appear during events that are supposed to last a certain amount of time (Blood Moon, Rain, Slime Rain (only if less than 75/150 slimes are killed), Sandstorm, and Solar Eclipse).
Note that invasions seem to require that at least one NPC is nearby; if an invasion's progress bar disappears beyond a certain distance, it may be necessary to place a house near the area. The game only checks horizontal distance to the NPC; you can house them far above or below your arena.
There are currently 14 () / 11 () / 8 () different events and invasions.
All of the events of Terraria except the Party event on the PC version, Console version, Mobile version, tModLoader version, and tModLoader 1.3-Legacy version, created to celebrate Terraria's 5th birthday, spawns unique enemies.
Pre-Hardmode
The Blood Moon is rising...
11.11% chance of occurring every night
The Blood Moon is an event that lasts an entire night. It has a chance of happening as soon as one player in the world has 120 health or more. During this event, the spawn rate of enemies and the maximum amount of enemies that can be on the screen at any time is increased. Enemies will also spawn near NPCs, even though they normally do not. It can be skipped using an Enchanted Sundial.
During a Blood Moon, Zombies and Werewolves can open doors after a few hits.
Special enemies spawn in addition to the usual enemies of the surface biome the player is in. The following enemies spawn during a Blood Moon:
Deathweed, which can be found in The Corruption/Crimson, will also bloom during a Blood Moon.
All water in the world (aside from the Ocean, Fish Bowls, and Water Fountains), including rain, gain a blood red color, similar to the Crimson's natural water color.
A Goblin Army has arrived!
Summoned with a 
Goblin Battle Standard
The Goblin Army is an event that has a 1 in 3 chance of occurring every dawn if at least one Shadow Orb/Crimson Heart has been destroyed, at least one player has 200 health or more, and there is not a Goblin Army already in progress. It can also be summoned manually using a Goblin Battle Standard.
During the event, five ( six during Hardmode) different types of goblins will spawn:
Although they do not appear in the Goblin Army, Goblin Scouts can be found rarely on the outer thirds of the map. They drop Tattered Cloth which is used to craft the summoning item for this event.
The event is completed after a certain number of goblins has been defeated. Afterwards, the Goblin Tinkerer NPC will spawn underground.
Occurs randomly
Rain can occur in any surface biome, changing the theme music and background, as well as dimming the lighting. Goldfish walk on land, and some different enemies spawn. Once the rain has ended, the effects fade away and the affected biome returns to normal. Rain in a Snow biome becomes a blizzard.
Rain always lasts 24 in-game hours.
The following enemies spawn during rain:
Flying Fish- Umbrella Slime
- Raincoat Zombie
- Angry Nimbus(Hardmode)
- Rainbow Slime(Hardmode Hallow)
- Ice Golem(Hardmode Snow)
Waterleaf plants, found in the Desert, will bloom during rain. Furthermore, NPCs will remain in their houses and all players are granted a +20% boost to their Fishing Power.
Slime is falling from the sky!
Occurs randomly
Slime Rain is an event that can only occur as soon as a player has at least 140 health and 8 defense (except in Expert mode, where it can occur with a significantly decreased chance before meeting the criteria). During the event, different variations of slimes constantly fall from the sky until the day or night is over. If the player kills 150 slimes (75 if King Slime was previously defeated) before the event ends naturally, King Slime will spawn.
Many types of slimes spawn, including:
Initiated by activating a 
Party Center
The Party is an event that causes most NPCs to wear a Party Hat, sell unique items, and display unique quotes. The event can occur randomly and will always end upon dusk.
The Party is the only "peaceful" event, not causing any additional enemies to spawn.
Occurs randomly
A Sandstorm only affects players in a Desert. During a Sandstorm, the Mighty Wind debuff will be inflicted, pushing all creatures afflicted with it in the direction of the wind, and particles will appear in the dusty yellow background. Sandstorms can also occur in Hallowed, Corrupted, and Crimson Deserts.
In addition to regular Desert enemies, the following enemies will spawn: Template:Item/options
- Angry Tumbler
- Tomb Crawler
- Sand Shark(Hardmode)
- Dune Splicer(Hardmode)
- Sand Elemental(Hardmode)
- Crystal Thresher
- Bone Biter
- Flesh Reaver
The Old one's army is approaching!
Initiated by placing an 
Eternia Crystal on an 
Eternia Crystal Stand
The Old One's Army is a unique Dungeon Defenders 2 crossover event that can be initiated after rescuing the Tavernkeep, who spawns after defeating the Eater of Worlds/Brain of Cthulhu. The objective is to protect the Eternia Crystal from waves of enemies seeking to destroy it. If the Crystal is destroyed, the event terminates. If it is kept "alive" until all waves are cleared, the event is defeated.
Both the Crystal and its Stand are purchased from the Tavernkeep NPC for coins. Players are inflicted with the Creative Shock debuff for the duration of the event, which prevents the removal or placement of blocks during the entire event.
Each wave becomes progressively more difficult. If triggered before any Mechanical Bosses have been defeated, the event consists of 5 waves. If triggered after at least one Mechanical Boss is defeated, the event consists of 7 waves. Once Golem has been defeated, the event becomes even more difficult with the boss Betsy spawning in the final wave. Only one Betsy will spawn during each invasion and defeating it will complete the event. The event also contains 2 mini-bosses, the Ogre and the Dark Mage.
The following enemies are exclusive to the event: Template:Item/options
Hardmode
The Frost Legion has arrived!
Summoned with a 
Snow Globe
The Frost Legion is an event that functions similarly to the Goblin Army, but it requires an item to start the event, which is only attainable in Hardmode. During Christmas, enemies will drop presents. If the world is in Hardmode, these presents have a 1 in 13 chance of containing a Snow Globe, which is used to spawn the Frost Legion.
During the event, three different types of unique snowmen will spawn:
All of the snowmen drop Snow Blocks, technically granting the player a way to obtain infinite amounts of Snow.
The event is completed after a certain number of snowmen has been defeated. Afterwards, the Santa Claus NPC will spawn during Christmas.
A Solar Eclipse is happening!
Summoned with a 
Solar Tablet Fragment
The Solar Eclipse is a Hardmode event that has a 1/20 chance to occur each day upon dawn, as soon as any Mechanical Boss has been defeated. The sun will rise, obscured by the moon, dramatically reducing natural light to a level darker than nighttime. Normal biome enemy spawns are replaced with special enemies that can spawn near NPCs, and spawn much more frequently and in greater numbers than usual. On the PC version, Console version, Mobile version, Old Chinese version, tModLoader version, and tModLoader 1.3-Legacy version, it can be skipped using an Enchanted Sundial.
The enemies that spawn during a Solar Eclipse at the start of Hardmode are as follows:
After all three Mechanical Bosses have been defeated:
After Plantera has been defeated:
A Solar Eclipse is always terminated upon dusk.
The Pirates have arrived!
Summoned with a 
Pirate Map
The Pirate Invasion is an event that is very similar to the Goblin Army. It can spawn randomly, or be summoned by the use of a Pirate Map, which can be obtained from killing any enemy in the Ocean biome during Hardmode.
During the event, seven / six different enemies themed around a pirate crew will spawn:
The event is completed after a certain number of pirates has been defeated. Afterwards, the Pirate NPC will move in.
Summoned with a 
Pumpkin Moon Medallion
The Pumpkin Moon is a Halloween-themed event that can only be summoned at night with the Pumpkin Moon Medallion. Unlike most other events, the Pumpkin Moon takes place in distinct waves. There are 15 waves in total, which grow harder as the night wears on, culminating in the "Final Wave," which lasts for the remainder of the night. The Pumpkin Moon can be skipped using an Enchanted Sundial.
The Pumpkin Moon has seven unique enemies, in increasing order of difficulty:
Although there are no rewards for surviving the event, the enemies can drop unique items, including Spooky Wood and equipment like the Spooky Hook and Raven Staff.
Summoned with a 
Naughty Present
The Frost Moon is a Christmas-themed event similar to the Pumpkin Moon that can only be summoned at night with the Naughty Present. It uses the same wave system as the Pumpkin Moon. The Frost Moon also has an additional five "bonus waves" after the "Final Wave", increasing the wave maximum to 20. Enemies have similar behavior to Pumpkin Moon counterparts, but are tougher, making this event the hardest on the 
Old-gen console version, 
Windows Phone version, and Nintendo 
version. The Frost Moon can be skipped using an Enchanted Sundial.
It has 11 types of enemies:
Although there are no rewards for surviving the event, the enemies can drop unique items.
Martians are invading!
Initiated by letting a 
Martian Probe escape
The Martian Madness event is a post-Golem event. It is unique from the others in that in order to start it, it is required to encounter a Martian Probe randomly in the outer parts of the surface and space levels of the world and move into its light. Once the probe detects the player, it needs to leave the screen without being destroyed.
The Martian Madness event features eleven unique enemies: Template:Item/options
The event is completed after a certain number of Martians has been defeated.
Celestial creatures are invading!
Initiated after defeating the Lunatic Cultist
The Lunar Events is a unique type of event that spawns four different pillars, the Celestial Pillars, spread evenly across the world. While in the proximity of a pillar, respectively-themed enemies spawn. There are four different pillars: the Solar Pillar, the Vortex Pillar, the Nebula Pillar, and the Stardust Pillar. Initially, all pillars are surrounded by a protective barrier. In order to damage and eventually defeat a pillar, a certain number of enemies of that pillar needs to be defeated.
There are numerous unique enemies in this event:
Template:Item/options
History
- Desktop 1.3.4: Old One's Army event added.
- Desktop 1.3.3: Sandstorm event added.
- Desktop 1.3.2: Party event added.
- Desktop 1.3.0.1: Martian Madness, Slime Rain, and Lunar Events added. Invasion Events now have a progress bar, showing how far along the player is towards completion. Event enemies now run away when the event is over.
- Desktop 1.2.4: Fixed bug where spawn rates would increase underground when a moon event is happening. Invasion summon items will no longer be consumed if no invasion would happen using it.
- Desktop 1.2.3: Invasions can now spawn enemies anywhere near friendly NPC instead of just the middle of the world.
- Desktop 1.2: Solar Eclipse, Rain, and Pirate Invasion events added.
- Desktop 1.1.1: Frost Legion event added.
- Desktop-Release: Introduced Goblin Army and Blood Moon.
- Console-Release: Introduced Goblin Army, Blood Moon, and Frost Legion.
- Mobile-Release: Introduced Goblin Army, Blood Moon, and Frost Legion.
- 3DS 1.03: Frost Moon Added.
- 3DS-Release: Introduced Goblin Army, Blood Moon, Frost Legion, Solar Eclipse, Rain, Pirate Invasion, and Pumpkin Moon.
- Pre-Hardmode Enemies
- Hardmode Enemies
- Event Enemies
- Bosses
- Critters
- Friendly NPCs
- Familiars
- Anomura Fungus
- Antlion
- Bat
- Bee
- Blood Crawler
- Crab
- Crimera
- Demon Eye
- Devourer
- Eater of Souls
- Face Monster
- Fungi Bulb
- Giant Worm
- Granite Elemental
- Granite Golem
- Harpy
- Hoplite
- Hornet
- Jellyfish
- Man Eater
- Meteor Head
- Mushi Ladybug
- Piranha
- Skeleton ()
- Shark (
- Orca
-
- Slime
- Snatcher
- Snow Flinx
- Tomb Crawler
- Undead Viking
- Vulture
- Wall Creeper
- Zombie
- Angler Fish
- Angry Trapper
- Arapaima
- Armored Skeleton
- Armored Viking
- Bat
- Black Recluse
- Blood Feeder
- Chaos Elemental ()
- Clinger
- Corruptor
- Derpling
- Digger
- Floaty Gross
- Gastropod ()
- Giant Fungi Bulb
- Giant Tortoise (
- Ice
-
- Herpling
- Ice Elemental
- Ichor Sticker
- Icy Merman
- Jellyfish
- Jungle Creeper
- Moss Hornet
- Pigron
- Pixie
- Possessed Armor
- Skeleton Archer
- Slime
- Unicorn
- Wandering Eye
- Werewolf
- Wraith
- Wolf
- Alien Skater
- Baby Dinosaur
- Baby Eater
- Baby Face Monster
- Baby Grinch
- Baby Hornet
- Baby Imp
- Baby Ogre
- Baby Penguin
- Baby Red Panda
- Baby Skeletron Head
- Baby Snowman
- Baby Truffle
- Baby Werewolf
- Black Cat
- Bunny
- Cursed Sapling
- Destroyer-Lite
- Dynamite Kitten
- Eater of Worms
- Estee
- Everscream Sapling
- Eyeball Spring
- Fennec Fox
- Flying Piggy Bank
- Glittery Butterfly
- Hoardragon
- Honey Bee
- Ice Queen
- Itsy Betsy
- Lil' Harpy
- Lizard
- Mini Minotaur
- Mini Prime
- Moonling
- Parrot
- Phantasmal Dragon
- Plantera Seedling
- Plantero
- Puppy
- Propeller Gato
- Rez and Spaz
- Sapling
- Shadow Mimic
- Shark Pup
- Skeletron Jr.
- Slime Prince
- Slime Princess
- Spider
- Spider Brain
- Squashling
- Sugar Glider
- Suspicious Eye
- Tiki Spirit
- Turtle
- Tiny Fishron
- Void Bag
- Volt Bunny
- Zephyr Fish
- Bat
- Guinea Pig
- Slime
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