Fun little game. I love the visuals (but I love 1-bit aesthetic no matter what :P). 6220 was my highest score.
One suggestion for some variation. Just like how the dragon magic lets them be invisible (except in the water), what if they did the opposite by having an illusion of a dragon which can't be seen in the water. So you waste your time shooting at something that isn't real... Like it can't get hurt by arrows (arrows pass through) and it fades away just before reaching the castle or something :o