Sorry this isn't a combination of two animals, but what about grasshoppers that are the size of actual horses (we call them "meadow horses" in my language, that's why it came to my mind lol)
Or meat eating plants that can move and actually chase their prey. Either by moving on some sort of legs or by being intelligent and preparing huge traps that can catch large animals or even humans. Or they might strangle you like snakes.

There might be an acidic marsh with some sort of acid loving bacteria with psychadelic effects I imagine a place with colorful water, like when oil from a car leaks and it sometimes looks like a rainbow? And there would be psychadelic fume from bacteria around that.