Could this possibly have to do with all 3 (napalm zombies, the power and the water dragons)?
The power; do the napalm zombies only appear once the power has been turned on? I'm still not too familiar with Shangri La, so this may be untrue.
Naga Dragons (still unsure of the jump from dragons to naga dragons in the post, if someone would clear that up i'd love it); taking the napalm zombies through the water dragons' water (or the waterfall, waterslide, water in general) decreases its health to that of a normal zombie.
This all really ties to the napalm zombies a lot, also i'm unsure why they'd phrase it as a warning but hey, that's my two cents.