Either you activate it yourself by using Rain Dance, or in the event your opponent uses a Rain Dance/Rain-based team, your Kingdra will take advantage of it.
Just because it has Swift Swim doesn't mean you have to have Rain Dance on your team. It can simply be there to take advantage of an opponent's Rain Dance.
On its own, crits only have a 6.25% chance of happening. Unless you're investing in Crit chance, Sniper wont come into play that often.
Do you want 6.25% chance of an even bigger crit (if left uninvested), or do you want to be able to take advantage of Rain by being able to outspeed your opposition (especially if they also have Swift Swim Pokemon, or even better: when they don't, such as Hydration users). --- PSN: darkwolf7786, 3DS FC: 3454-0686-4576. Looking for Eevee or Ditto Friend Safaris! Add/PM Me.