Here is the full list of all 40 Shantae and the Seven Sirens achievements.
Complete the adventure!
Defeated the Empress Siren.
Deactivate all the Towers.
Defeated the fifth Siren.
Obtain all magical forms.
Complete a Ghostly Quest.
Learn all magical dances.
Defeated the fourth Siren.
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.
Reach Tree Town.
Defeated the first Siren.
Have three Monster Cards equipped at once.
Took the tour!
Obtain a Monster Card.
Complete the adventure with 100% completion!
Complete the adventure as quickly as possible!
Complete the adventure with 100% completion as quickly as possible!
Uncovered a possible threat.
Revitalize cellular functions.
Witness every magical outcome with Slimes.
Shock a circus squid.
Open all Shock Machines.
Unearth a buried treasure.
Unearthed all secrets.
Upgrade all magic to max.
Avoid startling the Lobster Girl throughout the adventure.
Collect all Monster Cards.
Win the highest total in a Hula Contest.
Complete the game without any Health upgrades and all Heart Squids collected.
Complete the game in Beginner or Definitive Mode.
Complete the game in Rule Breaker or Full Deck Mode.