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