Here is the full list of all 46 Rusted Moss achievements.
Achieve ending C in speedrun mode under target time.
Achieve ending A in speedrun mode under target time.
Beat game in 2 hours
Get first Titania piece from Maya
Clear the game with less than 4 Titania pieces
Beat the game without talking to the Seer
Reached Ending A
Beat every boss in a single run
Survive Eli and Nell's fight
Fully upgrade gun.
Get all upgrades
100% the game
Defeat Pestilence
Defeat Ameli
Defeat Bonnie
Get all trinkets
Discover the full map
Beat all climb challenges
Clear Juni's Climb Challenge
Reached Ending D
Construct Titania
Read all the lore boxes
Reached Ending C
Reached Ending B
Return The Face
Clear Fern's Climb Challenge
Defeat Spirella
Join the Tea Party
Defeat Famine
Get all the guns
Defeat Maya
Defeat War
Clear Ameli's Climb Challenge
Get a Gift from Abby
Defeat Freia
Defeat Face Stealer
Clear Shopkeeper's Climb Challenge
Clear Seer's Climb Challenge
Defeat Void Worm
Defeat Lenore
Defeat Elicia
Find your first hidden note
Get Shot With a Huge Laser by Maya
Reach the lowest area in 15 minutes.
Get all achievements
Achieve ending D in speedrun mode under target time without giving the Seer any Titania Pieces.