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