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