Here is the full list of all 30 ASTRONAUTILUS achievements.
Get one of each kind of bomb
Trigger a CYCLEFISH with a SHELLFISH
Neutralize a PHAGE'S death node with a DIODE
Get a pack of CHUM to follow you
Kill a boss in under 20 seconds with 60+% POW
Kill a boss in under 20 seconds with 60+% DMG
Get max pearl rewards from 3 CRYSTAL MINES
Get max pearl rewards from 3 COILFRAMES
Buy 4 discounted items from a shop
Use all 8 weapons in a run
Enter POLAR
Enter ARRAYS
Enter SEPTIC
Enter RELAYS
Enter THERMAL
Enter LATTICE
Get a hitless reward from a boss
Meet the first shopkeeper
Meet all the shopkeepers
Trade with a slug
DESCRIPTION
Unlock MANTLEGATE
Beat MANTLEWYRM
Get 50% POW
Reach 100% POW
Get a 500+ pearl chain
Get a 1000 pearl chain
Trigger MANTLEWYRM'S failsafe on its first phase
Trigger MANTLEWYRM'S failsafe on its second phase
Buy a cosmetic