Have you talked to the painter on the next screen (armor room) yet?
You should know that Amoniak likes ladybugs, and you should learn where to put them so that he'll eat them.
The catch is that there aren't any ladybugs anywhere in this episode. You need to create some fake ladybugs to fool Amoniak into eating them.
It first might help to start with another insect, one like a ladybug.