Here is the full list of all 15 Boss trophies - there are 13 bronze, 1 silver and 1 gold.
Reach level 25
Beat the third castle of Trogon Kingdom on Hardcore
Get 9 evolutions
Buy 40 items
Reach 250 score on the arena
Reach 15000 Score on Falling Heroes
Beat Santa’s Workshop
Reach 5000 Score on Run Hero Run
Freeze 14 enemies simultaneously
Beat the Haunter Factory
Burn 14 enemies simultaneously
Survive an explosive princess
Make 50 hits with an object
Reach a 99 hit combo
Poison 10 enemies simultaneously