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