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