Ugh. I just scraped by on credit #4! The dung beam attack is really hard to counter--I did it once out of four times I encountered it. I think it's probably better to be proactive and take out the dung ASAP with a preemptive beam.
The stage itself is easier than stage 2. The reflective guys have cool interplay, since they shoot your beam back at you in diagonals.
For the final vertical stretch, if you don't mind missing out on a ton of points, hang out at the very top. Barely anyone will go for you there.
In general, this game has a neat sense of interplay. The idea of a beam duel itself is an alternate way of interacting with bosses, and there are some meaty projectiles you can take out with your main shot (mainly missiles and meaty shots like those from the first stage 2 miniboss).