Here is the full list of all 123 Cassette Beasts achievements.
Obtain 120 different species
Obtain a Metal-type bootleg
Enter a romantic relationship
Open a door long since thought lost.
Get to 5 hearts with Viola
Complete 20 noticeboard quests
Obtain a Fire-type bootleg
Meet the Travelling Merchant
Get to 5 hearts with Barkley
Obtain a Beast-type bootleg
Defeat an Unstable Fusion
Get to 5 hearts with Kayleigh
Obtain 100 different species
Get to 5 hearts with Meredith
Defeat 50 Rogue Fusions
Observe 120 different species
Complete 5 noticeboard quests
Obtain Candevil
Get to 5 hearts with Felix
Obtain a Glitter-type bootleg
Obtain the Averevoir Flight ability
Get the Fusion Radar
Defeat Ianthe and become a Ranger Captain
Get to 5 hearts with Eugene
Defy all odds in a place between worlds.
Solve the riddle of Morgante's song.
Reopen every station
Complete Felix's quest
Meet Kuneko at 4 altars
Meet Kuneko at 3 altars
Meet Kuneko at 2 altars
Defeat 20 Rogue Fusions
Meet Kuneko at 1 altar
Defeat Lamento Mori
Defeat Captain Cybil
Help Sunny start a new life
Defeat Captain Lodestein
Defeat Captain Codey
Defeat Captain Buffy
Complete Eugene's quest
Complete Morgante's song
Defeat Captain Heather
Defeat Babelith
Visit every part of New Wirral
Clear 5 Landkeeper offices
Clear 4 Landkeeper offices
Win a battle before it starts
Defeat Captain Judas
Defeat Alice
Defeat Captain Gladiola
Find a helping hand in a place far away.
Find yourself somewhere far away.
Defeat Heckahedron
Defeat Poppetox
Complete Viola's quest
Bring Viola to the shipwreck
Complete Barkley's quest
Obtain an Ice-type bootleg
Unlock Barkley
Unlock Viola
Meet Kuneko
Obtain the Pumpkin Vine Ball ability
Defeat Captain Skip
Obtain 50 different species
Complete Kayleigh's quest
Try to sneak past a battler by jumping over their head
Unlock Felix
Obtain a Plastic-type bootleg
Defeat Captain Clee-O
Defeat Captain Zedd
Clear 3 Landkeeper offices
Defeat 10 Rogue Fusions
Complete Meredith's quest
Defeat a ghost
Help Hoylake with his research
Clear 2 Landkeeper offices
Defeat a Swarm
Bring Meredith to the mall
Defeat Captain Penny Dreadful
Obtain the Bulletino Dash ability
Obtain the Diveal Swim ability
Defeat 5 Rogue Fusions
Obtain the Electromagnetism ability
Obtain 20 different species
Obtain a rare sticker
Unlock Meredith
Choose a design for Harbourtown's sign
Meet the one who dutily attends the stations.
Investigate a rumour
Clear 1 Landkeeper office
Unlock Eugene
Obtain a rumour
Defeat Captain Wallace
Obtain 10 different species
Sign up to the Rangers
Remaster a tape
Start Kayleigh's quest
Defeat a Rogue Fusion
Complete the tutorial
Obtain the Mothwing Glide ability
Unlock Kayleigh
Obtain Bansheep
Defeat an Orb Fusion
Obtain additional data on every species
Obtain a Plant-type bootleg
Obtain a Water-type bootleg
Obtain a Poison-type bootleg
Obtain an Astral-type bootleg
Obtain a Lightning-type bootleg
Obtain an Air-type bootleg
Obtain an Earth-type bootleg
Obtain a Glass-type bootleg
Obtain a monster form thought impossible to find.
Defeat an ancient force brought back to full strength.
Overcome the essence of fusion.
Come face-to-face with a faceless being.
Complete Frankie's training
Complete Vin's training
Complete 50 noticeboard quests
Complete 100 noticeboard quests
Win a battle while ghostly
Win a battle while Gambit is active
Prove your worth to a certain warrior.