Here is the full list of all 58 Day of the Tentacle Remastered achievements. It takes around 3-4 hours to unlock all of the achievements on Windows.
Get all other achievements in the game
Sit through the end credits
Play the whole game without skipping a cutscene
Defeat Purple Tentacle yesterday
Reach yesterday without turning the stereo off
Power Hoagie's Chron-o-John
Hoagie uses battery with Chron-o-John instead of plug
Red makes a super battery with only a little help from Hoagie
Power Laverne's Chron-o-John
Vacuum up a hamster
Cook the hamster in Maniac Mansion (Don't try this at home, kids!)
Ring the front desk bell 100 times
Try to flush the hamster
Flush 50 objects through time
Laverne thinks about eating the cat
Pick up 45 things that don't belong to you
Make a skunk
Win the human contest
Disqualify Harold
Make vinegar
Acquire a diamond
Try to microwave the hamster again after he's thawed out
Microwave the frozen hamster
Talk to Washington, Jefferson, or Hancock while they're outside
Laverne tries the chattering teeth on her human during the human show
Enter the human contest
Talk to Dead Cousin Ted with all three kids
Clothe Laverne in the costume
Deflate Oozo
Get all six novelty items
Change the flag
Climb through the chimney with all three kids
Get a tiny sweater
Get Fred to sign the contract
Wake up Dr. Fred
Try to sign the contract yourself with the quill pen
Destroy a cherry tree
Try to wash the dirty car with the brush
Try to mix the red paint and the Booboo-B-Gone
Try to alter the contract with Booboo-B-Gone
Create a cherry tree
Make it rain
Hoagie eats a Hoagie
Try to swap the textbook with the stamp album
Try to put something metal in the microwave
Try to mix the disappearing ink with Booboo-B-Gone
Turn off the television
Try to mix the decaf and caffeinated coffees
Squirt five different people with disappearing ink
Ask the IRS agents if they're related
Return the stamp album to Weird Ed
Get a job
Open the safe
Pick up 30 things that don't belong to you
Play Maniac Mansion
Pick up 15 things that don't belong to you
Close a door
Find Fred's basement workshop