Progression Stages

"'Your actions have consequences.'"
 * Rebirth of the Night's progression is divided into various stages that trigger once a condition is met. These conditions include defeating certain bosses and minibosses, mining certain ores, and visiting new dimensions. The effects of gamestages include harder mobs spawning, new ores being unlocked, and more types of quintessence being released by magicite.

Multiplayer Note
Some progression stages are global, affecting all online players, some are not. Personal growth stages (early game armor and mid-game armor) only affect the player who got the achievement. All other stages affect the entire world, meaning all online players. If you are playing on a server and not teaming up with players, it's recommended that you advise them to log off while you complete a progression stage, so that newer players do not unlock them. Obviously, this only matters if the players are far away from each other.

If a player logs on for the first time after all the stages are unlocked, they won't have any of the progression stages, meaning progression mobs won't spawn around them if other players are far away. They can still unlock all stages themselves.

Nether
"Cries of the damned echo around you..."

New Mobs

 * Salamanders can now spawn below y=48 in the Overworld
 * Magma Grunts can now spawn below y=40 in the Overworld and Beneath
 * Embers can now spawn below y=50 in the Overworld
 * Fire Creepers, Zombies, and Skeletons can now spawn in the Overworld
 * Strawberry Slimes can now spawn on the surface during the day

Other Effects
The following mobs can now spawn with golden armor:
 * Zombies
 * Skeletons
 * Skeleton Warriors

Aether
"A cool breeze fills the air..."

New Mobs

 * Kelenks can now spawn at night above y=80 in the Overworld
 * Lemon Slimes can now spawn on the surface during the day

Beneath
"Shadows squirm and writhe around you..."

New Mobs

 * Undertakers can now spawn at night in the Ominous Woods, Wasteland, and Dead Forest biomes
 * Zotzpyres can now spawn underground below y=100
 * Death Creepers can now spawn in the Overworld
 * specialmobs:dark_creeper can now spawn in the Overworld
 * specialmobs:undead_witch can now spawn in the Overworld
 * specialmobs:blinding_silverfish can now spawn underground below y=80
 * specialmobs:poison_silverfish can now spawn underground below y=80
 * Plagued Zombies can now spawn in the Overworld
 * specialmobs:poison_skeleton can now spawn in the Overworld
 * Skeleton Knights can now spawn in the Overworld
 * specialmobs:poisonspider can now spawn in the Overworld
 * Rats can now spawn in the Overworld
 * Undead Swine can now spawn in the Overworld
 * Frigids can now spawn in frozen biomes in the Overworld
 * Overgrown can now spawn in lush biomes

Other Effects
Zombies and Goblins can now spawn holding the following:
 * Mythril Pickaxe
 * Onyx Pickaxe
 * primitive_mobs:goblin_mace

End
"You feel empty. You hear nothing. You want to leave." No changes are made until after the dragon is defeated

Twilight Forest
"You hear a terrifying roar in the distance..."

First Mythril
"'The darkness erupts with distant screeches as the last magic barrier shatters...'"

Effects:
 * Invasions


 * All Dimensions


 * Overworld, Beneath, Nether, and End


 * Overworld, Beneath, Nether


 * Overworld and Beneath


 * Overworld


 * Aether

Harvester (Rebirth of the Night)
"'Deadlier mobs now roam the world at night'"

Other Effects
"'The next night will bring a bountiful harvest.'"
 * The next night will be a guaranteed Harvest Moon.

Quazar (Rebirth of the Galaxy)
"'The ground shudders deep beneath the planet'"

Wither (Rebirth of the Nether)
"'Voices of lost souls scream in fury...'"

Other Effects

 * Dormant Onyx is no longer dormant and can be mined

Ender Dragon (Rebirth of the World)
"'Fragments of a lost empire echo around you...'"

Ghast Queen (Rebirth of the Forest)
"'Visions of mythical beings flash through your mind...'"

Fonts of Magic
The death of certain powerful creatures causes certain types of quintessence to be released into the overworld. The quintessence can then be obtained by mining specific colors of magicite.

Trivia

 * The status messages seen in the chat are inspired by Terraria.
 * This feature used to be on a difficulty meter.