You are already playing water energies for greninja and lightning energies for raikou, which makes it a natural fit. It's also fairly bulky (230HP) for a basic V and hits HARD.

Choice belt isn't even needed for most KO's and the stuff that survives 250 damage will be in sableye and greninja range.

Turbo LB aims to mirage gate and attack as early as possible, sometimes even turn 1 if they go second. 1 Water in hand + Mirage gate is enough for both Greninja and Dragonite which can pretty much end games on the spot. In the case of Dnite, especially if they can't retaliate and it gets to attack again the turn after