Okay, first battle! 8D I'll be using Gabriel, my Frillish.
] Frillish ♂
Gabriel, let's start off with a Confuse Ray. If he happens to taunt you before you can confuse him, go with an Ominous Wind and try for the stat boost. If he protects, set up a Trick Room. Then, if you haven't already, get the Trick Room up; if you did manage to, attack with a Shadow Ball.
Confuse Ray/Ominous Wind/Trick Room ~ Trick Room/Shadow Ball