Here is the full list of all 27 Scribblenauts: Showdown trophies - there are 8 bronze, 12 silver, 6 gold and 1 platinum.
Create a custom Scribblenaut.
Earn 25 Starites.
Win 5 consecutive games against a single player.
Unlock all other trophies.
Play every Wordy game at least once.
Play every Speedy game at least once.
Create all 15 custom Scribblenauts.
Earn 100 Starites.
Create one of Maxwell's brothers in Sandbox Play or a Wordy game.
Play Sandbox with two players.
Create 100 Sandbox objects.
Complete a Showdown with 4 players.
Complete a 9 round Versus match.
Complete a 15 round Versus match.
Complete a 25 round Versus match.
Shutout a player in Versus by winning every single round.
Score at least 1500 points in Drone Drop!
Create a chain of 10 objects in Rocket Rubble!
Knock down a tower in 8 launches in Tower Topple!
Win a game of Get Served! without losing any health.
Make it to the finish line in Take Flight! with full health.
Win a game of Super Sprint! without hitting an obstacle.
Win a game of Balancing Act! without dropping any of your objects.
Unlock all 8 Sandbox levels.
Unlock all the custom Scribblenaut parts.
Unlock all custom Sandbox objects.
Unlock all vehicles in the game.