Is it officially stated that bosses drop more in lower venues? As that isn't my experience. I have gotten like a dozen Mantarunes and Wave Sweepers (not exaggerating at all), but I have yet to get any other boss. And it's not like I spend a lot of time in the Kelp Beds. I did a reasonable amount, but not that much more. In fact, when I trained teams to 25, I'd spend the last handful of levels in the Mire, skipping the Kelp Beds entirely, as I wanted the damn toads. Which I still don't have.