I think it's possible for a pond snail or if you have a half water setup maybe some Fathead Minnows. But you would have to clean a lot. Fish poop a lot. Possibly a North American Millipede if it's large enough and if you have the water raised to the point to where it couldn't get in than it should work. Possibly a bunch of Woodlice. If you use a frog or toad the frogs would most likely get eaten. If you use a lizard it probably would get poisoned. Grey Tree Frogs are very toxic. So there isn't much to really encourage. I hear of Green Tree Frogs sharing the enclosure. But they have different requirements. If you are gong to do it any way, I wish you good luck. I am not against mixing species because I have a mixed tank of Eastern American Toads and Northern Leopard Frogs. It's at my own risk. They occupy different niches in a 75 Gallon Aquarium. You must research before you go off of what anybody says anywhere because you are the one who is keeping them. Research and experience with other species is key. So things that would not be able to live in a similar environment don't get put in that position. IMO. Good luck
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