Here is the full list of all 31 Stranger Things 3: The Game achievements.
Beat the game on New Game+
Complete the game
Complete Mall Showdown
Found all 50 hidden gnomes.
Complete Cabin Ambush
Complete Invasion of Privacy
Complete 30 Minutes or Less
Unlock Steve
Unlock Erica
Complete Hospital Brawl
Found 25 hidden gnomes. Half-way there!
Unlock Will
Unlock Hopper and Joyce
Complete Chores for Granny Perkins
Successfully hack the hardest level chest/door
Unlock Eleven
Complete Revenge of the Geeks
Unlock Max
Complete Ivan the Smuggler
Craft 5 trinkets
Complete Break In, Make Out
Unlock Jonathan
Unlock Nancy
Complete Store Raid
Complete Wall Flower
Complete Rats in the Walls
Complete On the Wire
Complete Radar Love
Crafted your first item
Unlock Dustin
Complete Sneak Peek