Here is the full list of all 40 Shantae and the Seven Sirens achievements.
Unearthed all secrets.
Collect all Monster Cards.
Upgrade all magic to max.
Open all Shock Machines.
Complete the adventure as quickly as possible!
Complete the adventure with 100% completion as quickly as possible!
Complete the game in Rule Breaker or Full Deck Mode.
Complete the adventure with 100% completion!
Complete the game in Beginner or Definitive Mode.
Complete the adventure!
Defeated the Empress Siren.
Complete the game without any Health upgrades and all Heart Squids collected.
Deactivate all the Towers.
Avoid startling the Lobster Girl throughout the adventure.
Defeated the fifth Siren.
Obtain all magical forms.
Shock a circus squid.
Witness every magical outcome with Slimes.
Complete a Ghostly Quest.
Unearth a buried treasure.
Learn all magical dances.
Defeated the fourth Siren.
Revitalize cellular functions.
Locate the sunken ship remains.
Fell for a double cross.
Open a Shock Machine.
Ascend to Armor Town.
Defeated the third Siren.
Turn an enemy to an ally by helping them heal.
Enter the Sea Lab.
Obtain the Lucky Amulet.
Defeated the second Siren.
Use the valve.
Uncovered a possible threat.
Win the highest total in a Hula Contest.
Reach Tree Town.
Defeated the first Siren.
Took the tour!
Have three Monster Cards equipped at once.
Obtain a Monster Card.