...What if poison types got an ability called "Acid Rain" (not the glitch) that activates during a rainfall? This ability pollutes the rain and boosts the power of poison type moves by 50% instead (and may or may not restore the poison type's HP by 1/16 or decrease non-poison type's HP by 1/16 each turn it's activated).
So the ability lets poison types steal rainy weather from water types to use for their own benefits. Abilities like Rain Dish and Swift Swim won't work during Acid Rain, and water type moves lose the 50% attack boost.
I was also thinking that when Acid Rain activates, the water is polluted every other turn instead of every turn until the rainfall ends. The water will be polluted during the turn when Acid Rain activates, then it will be clean the next turn, then it will switch back again. So the benefits constantly change between water and poison types.
Another thing to note would be if Drizzle is activated or Rain Dance is used during Acid Rain after a Pokemon with Acid Rain is switched out, the water will become clean again.
Another alternative would be instead of Acid Rain relying on the weather becoming rainy in the first place, Acid Rain can either be an ability that works like Drizzle or a move that works like Rain Dance. So, just a weather that benefits poison types.
How does this idea sound? It gives poison types a buff without changing the SE table. I won't mind if you think it's a crappy idea, please just state why you feel that way, any improvements that can be made to the idea, or if it doesn't belong at all. Also, terrible sorry if this is an old idea!
Acid Rain should just be a separate weather that damages all Pokemon not of the Poison and Steel types. Definitely would boost the power of Poison moves. Could possibly guarantee success with Gunk Shot (AKA Poison-type Thunder).
someone here had a similar idea once, which also included removing steel's immunity to poison. that'd be cool. --- Official Ninetales of the Pokemon X and Y boards PokeDoc: http://tinyurl.com/mustardpi314