My conclusion on Gravity and RainDance in conjunction.

Thunder is more than 100% accurate in the rain. It doesn't even go through an accuracy check. It just HITS. 25% chance to break Protect and Detect.

If you switch in an obvious Thunder user into Gyarados, there's a good chance they'll switch to something that's immune or resistant to it. Hippowdon fucks your pomegranate up with a Thunder immunity and Sand Stream.

Well, thing is, would you expect Thunder from Jirachi? Good chance it does if I'm switching it out @ Gyarados. However, then assuming they do switch to Hippowdon, so what? Ok, Sandstorm negates Rain Dance instantly. So Jirachi sets up Gravity. What can Hippowdon do? Spam STAB'd EQ? Unless it's an Adamant nature one with maxed att EVs, I'm not too worried. I'll spam accurate-Dynamic Punches at it to confuse it, thus forcing the player to switch to something else, or he/she will use Roar at me. Technically, it could go either way here.