For clarity, you should also put in the OP that after Turn 6, switching in grounded Poison-types doesn't remove Toxic Spikes.
Anyway, this is possibly the best early-game support set for weather teams with an automatic weather inducer, such as Politoed or TTar:
Whimsicott @ Lagging Tail
Ability: Prankster
EVs: 248 HP / 252 Def / 8 SpD
Impish Nature
- Taunt
- Encore
- Trick Room
- U-turn
If you're running Sun, Rain, or Sand, you can't afford to have Trick Room up, so Trick Room is there to cancel out a Trick Room that's been set up and is most optimally used on Turn 5. Then, on Turn 6, you get a slow U-turn into your weather inducer, and thus your opponent has no way of removing your weather. Taunt and Encore are pretty obvious for this meta, and you want to force an opposing Trick Room user out by Turn 5 with them so that the field can be both devoid of Trick Room and with your weather permanently. Although, if you're in a situation where you have to choose between negating your opponent's Trick Room and setting up your weather, you should negate their Trick Room because if you're in a Trick Room-less, weather-less field, all of your Pokemon should be faster than your opponent anyway because your opponent has a Trick Room team.