Here is the full list of all 23 Hotel Transylvania 3: Monsters Overboard achievements.
Rescued Wayne.
Rescued Frankenstein.
Defeat the Fiendish Flower and retrieve the first part of Neptune’s Compass.
Defeat the Cruel Crustacean and retrieve the second part of Neptune’s Compass
Defeat the Dastardly Dragon and retrieve the final part of Neptune’s Compass
You’ve collected the first of many treasures.
Collect half of the Treasures hidden in the Lost Islands.
Collected every single Treasure hidden in the Lost Islands.
You’ve defeated 5 enemies in a single night.
Have 5 of each Impa type at once for more than 5 seconds
Collect 5 Imparite stones in a single night.
Defeat a Coconut Crab while it’s stunned.
You’ve safely retrieved an object from an angry Giant Clam.
Unlock the third Impa Portal.
Unlock half of all Impa Portals.
Unlock every single Impa Portal.
Have 30 Vampirimpas at once for more than 5 seconds
Defeat any enemy other than a Feeble Flower with nothing but a single Wolfimpa.
Defeat an enemy with the impact from a thrown Frankenimpa.
Use Mummimpa’s Magic Sand to block the smell trail from a Stinkbulb.
You’ve successfully liberated 3 objects from Giant Clams.
Hit an enemy with a ricocheted Mummimpa.
Complete the tutorial and meet up with Ericka.