Make bloated pearlfrogs rarely spawn in rivers

[John Snail]

Rivers are fairly non-threatening for the parts of the map they cover. The bloated pearlfrog is a similar level to the madpoles, and its gimmick would have a scary synergy with them (either pulling you into the river, or the madpoles out of the river). Maybe add a 15% chance for 1 bloated pearlfrog to spawn in river zones?

[Brian Bucklew]

fine but not tracked here