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