Here is the full list of all 21 Stacking achievements. It takes around 8-10 hours to unlock all of the achievements on Windows.
Completed all Hi-jinks in the Lost Hobo King adventure.
Found all solutions to all of the Lost Hobo King challenges.
Found all unique dolls in the Lost Hobo King adventure.
Completed the Lost Hobo King adventure.
Collected all unique dolls in the Triple Decker Tank Engine.
Completed all Hi-Jinks in the Triple Decker Tank Engine.
Collected all unique dolls in the Zeppelin of Consequence.
Completed all Hi-Jinks in the Zeppelin of Consequence.
Completed all Hi-Jinks in the Royal Train Station.
Completed the Final Challenge.
Completed the Triple Decker Tank Engine adventure.
Found all solutions to all of the Triple Decker Tank Engine challenges.
Found all of the solutions to all of the Royal Train Station challenges.
Found all solutions to all of the Zeppelin of Consequence challenges.
Completed the Zeppelin of Consequence Adventure.
Collected all unique dolls in the Royal Train Station.
Found all solutions to all of the Gilded Steam Ship challenges.
Collected all unique dolls in the Gilded Steam Ship.
Completed all Hi-Jinks in the Gilded Steam Ship.
Completed the Gilded Steam Ship Adventure.
Completed the Train Strike Adventure.