The Progression Shield is a feature added by the Twilight Forest. It has three different forms, with one being a giant mist of hollowed green squares, another being the same thing but a smaller variation and the third form isn't visible, but instead it inflicts an effect on the player.
It only appears at certain landmarks in the dimension if certain requirements aren't met, such as:
- Attempting to enter a Lich Tower without killing the Naga.
- Attempting to enter the Labyrinth without killing the Twilight Lich.
- Attempting to enter the Fire Swamp without killing the Minoshroom.
- Attempting to enter the Stronghold without killing the Hydra.
- Attempting to enter the Dark Tower without killing the Knight Phantom.
- Attempting to enter the Yeti Lair without killing the Ur-Ghast.
- Attempting to enter the Aurora Fortress without killing the Alpha Yeti.
The Progression Shield also has various effects on certain biomes when the requirements to access them are not met, some of which will also give a warning. They will inflict an effect on the player in some way, such as:
- Attempting to explore the Twilight Swamp will inflict Hunger on the player while being swarmed in a thick and dense black mist of mosquitoes.
- Attempting to enter the Fire Swamp will burn the player without any additional effects. Even if they bypass the fire by any means, they will not be able to progress.
- Attempting to enter the Dark Forest without killing the Hydra will inflict Blindness on the player while being swarmed in eerie-looking black wavy lines.
- Attempting to explore the Snowy Forest without killing the Ur-Ghast will inflict strong Slowness on the player while they are being swarmed in a thick blizzard.
- Attempting to explore the Highlands, Thornlands or Highlands Center without killing the Snow Queen will hurt the player with acid rain.
Attempting to break blocks or hurt enemies inside the Progression Shield will not deal any damage to the blocks or enemies.