[chrispenycate]

Starting with the menagerie, the satyr should be no problem, although hooves are better adapted to quadrupeds; keeping your balance on the tiny little surfaces shown in most illustrations would be akin to stilt walking. Check jack Chalker's satyrs from the "Well of souls" series (sorry, can't remember which volume; they've all melded together in my memory); they pretty well have to keep running all the time to stay upright.

Growing extra limbs is a fairly standard birth defect. If you got an arboreal predator, a marten perhaps that grew a balanced pair of limbs, instead of just vestigial, or singleton extremities, it could be quite successful, ultimately getting too big to climb trees, and taking up a plains existence. It's not much like a centaur yet, as it hasn't hooves like a horse (closer to human feet, tree gripping extremities modified for land locomotion) but it has got forward gripping manipulators strong enough that it could swing from a tree, and eyes set forward to concentrate on prey; it could take up archery well enough, if it became intelligent enough.
But is there the stimulus to develop intelligence (when sober, they're supposed to be wise and knowledgeable)? After all, if you're a good enough predator (Why predator? looking at all that body that's got to be fed through that little mouth I was reminded of the marsh-wiggle's description of a centaur's breakfast in "the silver chair", and wanted to get in food in as concentrated a form as possible, which means meat.) what's the use of intelligence?

For the mer-folk. I really think gills are impractical for mammals (and it is generally held that mermaids at least have mammalian characteristics, mermatrons presumably more so. To get enough oxygen out of water you would need an immense surface area of blood almost in contact with water (cube/square law), and this would call for a very low (and preferably variable) body temperature, or an enormously active metabolism, which would call for still more oxygen and thus more surface area…

If we allow them to be cold blooded, then we could use one organ for getting oxygen from either air or water; the two requirements are not that different, you just need more water. Perhaps slits above the collarbones, and a valve system forcing the fluid (air or water) out below the stomach?

I suppose the smaller, animistic gods (not much more than natural spirits, really) must have have power limits; but your major monotheistic or bipolar manacheean deities are essentially infinite power sources. Fortunately they're not matter; mutual annihilation of even a few kilograms of matter would render the Earth uninhabitable, and gods are reputed to be quite big. Indeed, mere conflicts of gods have been known to cause severe flooding and mountain ranges; a mutual elimination could cause just about anything in the way of effects.

But when it comes to tsunami production, standing on top of the ice sheet isn't a good way to go about it. Dropping ice sheets into the sea makes a nice splash, but it's localised; melting a few megatons of ice will bring the sea level up fractionally, but it's slow. Perhaps divine combat causes earthquakes; a nice submarine fault shift can get some water moving.

But have you considered holding the competition on thick sea ice, over a bay? As the the battle warms up, they melt a hole through the ice, ultimately finding themselves deep under it, with penguins wondering why there are flashes of light and vibration under their feet. The ultimate discharge vaporises a couple of cubic miles of Antarctic ocean, producing steam. Some manages to escape through the hole they came in through, throwing huge plates of ice (and penguins) kilometres into the air, but most doesn't, and the expanding cloud forces water out from under the plate ice, a shock wave which turns into a water wave the moment the sheet is thin enough to break up, ten, fifteen metres in height in the open ocean, five times that when it's impeded by anything solid, water warmed as much by friction as the original generating steam, with icebergs floating in it up to the equator, and further…

*Looks around. Sorry, must have got a bit carried away, there. I'll go and rhyme something, shall I?*