Hyper Beam isn't good on anything. Especially on something like Sceptile. Drop that for Substiture. Screech doesn't have much of a point either, since they just switch out after you use it. But if you tech in Focus Punch, I could almost see a use. Leech Seed just works so much better. The last replace ment I suggest would be dropping agility(Since he has one of the highest base speeds in the game). Try something like Focus Punch. If you can, breed to get one with a bold nature.

Naughty Nature. Substitute/Focus Punch/Thunderbolt/Ice Punch. Standard McGar. Also, Leftovers.

Sitrus Berry recovers like... a 10th of your health(and only once). Drop it for leftovers or Choice Band. There is no nature called cool. Get an adament one. Drop Crunch for Earthquake and poison fang for Sludge Bomb.
 

Timid Nature, Neutral natures don't help you at all. Drop Facade for something like HP:Grass and Rain Dance is a good final move, since it supports Swift Swim. Also, Hydrop Pump with STAB after Rain Dance hurts A LOT. Possibly try that instead of Surf.
 

I really suggest dropping this for something else. It has a horrible movepool, and mediocre stats. But if you insist on using it, drop Fly for Aerial Ace, Mirror move for HP:Ground, and Wing Attack for Double Edge. Lum/Liechi/Salac Berry works better, since this think is going to die and die fast.

Use Tyraniboah. Quiet Nature, Substitute/Focus Punch/Thunderbolt/Crunch. And if possible, max HP. Leftovers.