Here is the full list of all 13 Gutwhale (HK/TW) trophies - there are 1 silver, 11 gold and 1 platinum.
Get all other trophies
See the true ending
Kill up to 50 frogs (accumulative)
Beat the third level
Unlock the frog-hat
Get 100 points
Get a free point increase
Beat the second level
Kill your first skull enemy
Buy an upgrade
Beat the first level
Get a combo of 10
Get a combo of 5