I'm new to VGC but not to competitive, currently in Great Ball 2.
First thing off the bat I see is you only have Protect on one mon, and most of your guys have 4 attacking moves. You really should consider more Support attacks.
Primarina really should have Hyper Voice. Its ability Liquid Voice turns it from Normal type to Water type with STAB, and it hits both of your opponents.
We can't see your items, are you running Mega Garchomp? If not, maybe consider changing its ability since you're not running a Sand team. Rough Skin will let you do 1/8th damage to your opponent on contact moves. Honestly you should probably do this regardless, chances are that'll occur more often than benefitting from your opponent's Sand.
Clefable -- you have a nature that's reducing your Defense while investing EVs into it. Change this nature to something that lowers Attack.
Actually you're doing the same thing with your Garchomp, go with a Special Attack reducing nature for Garchomp.
Unless you're running Trick Room, generally you don't want to lower your own speed. Greninja, Snorlax, and Primarina's natures all are lowering their speed. Switch these natures to something lowering their unused attacking stat.