Actually, a Ninetales would make a great addition instead of Solrock. Ninetales's Hidden Ability is Drought, a move that causes Sunny Day forever so long as it is out. It knows Ghost moves and are known the be vengeful Pokemon that curse humans.
so we have Gyarados (The raging seas), Tyranitar (the crushing mountains), Ninetales (The Harsh Sun), what other natural forces are incredibly dangerous to humans? Swamps? Snow?
Ok, what I got are Tyranitar, Gyarados, Solrock could work in some cases, as it is a Sun, a natural Force, and a serious foe in the deserts. Muk is a Polution Pokemon, which would fit, but Muk is Poison, and would loose easily to Mew.
Oh whoops I was thinking of some strong, awesome bosses. Snorlax and Ursering could have an advantage over Mew depending on the moves that are taught to them.
Besides the ones already mentioned, I can't think of any based on natural disasters :\ Let me ask the others to see if they can think of some