At first, it was a bit confusing. But it became clearer after enemies started to drop some items and when I saw the word "Effect".
The experimentation process is very enjoyable. I like that the initial items and drops from enemies are random, it forces you to try different things and improvise different tactics.
My hypothesis is that the right-most card is close to the HP bar. So, sometimes the collision boxes are slightly overlapped and hence the occasional auto use of paint bucket.
There are hints in the pause menu at the top right of the screen that might help you figure out the ability of each enemy.
I agree, when there are all blues and buckets, it felt like no progress are being made.
About the paint bucket: Red bucket - heal the player Yellow bucket - attackers take some damage Blue bucket - block incoming damage
Actually, all colored spray cans are able to destroy any enemy. The differences are damage and special effect - there is no elemental attack in this game. Also, each enemy has different health.
