Here is the full list of all 42 Monolith achievements.
Finished a run with a score of 300,000.
Finished a run with a score of 200,000.
Take a screenshot containing 100 bullets.
Won without getting any upgrades.
Get all 4 S Ranks in one run.
Get an S Rank in Damage (10 hits or fewer)
Won the game on Sudden Death Lethality
Protect Blastcore's smile.
Won without getting any weapons.
Reach a highscore of 20 minigames in the Hub.
Get an S Rank in Exploration (Visit all rooms)
Won the game on Intense Lethality.
Get an S Rank in Time (Under 20 minutes).
Tarnish notte the majesty! (Acquired all Hats)
Become the reigning tag champion.
Get an S Rank in Secrets (Find all secrets)
This is what you wanted, isn't it?
Finished a run with a score of 100,000.
Pass the seal. (Floor 6)
Leave that poor cat alone.
Defeated the Overlord.
Reach the Sanctum (Floor 5).
Reach the Temple.
Reach the Bellows (Floor 4).
Reach the Maintenance System (Floor 3).
Reach the Archives (Floor 2).
Reach the Excavation (Floor 1).
Admire a fine portrait.