I'm going to suggest a setup that's fun and I would most likely pick. I usually just Wingull it when I playthrough games and never have ran into any issues.
Leech Seed
Solar Beam (or other powerful grass move)
Razor Leaf
For a last move I'd pick either of these
Sunny Day
Body Slam(Or other normal alternatives)
Giga Drain
When you play against the CPU, Leech Seed is just too good because they don't switch Pokemon. So eventually whatever you use it on will faint.
Leech Seed
Solar Beam (or other powerful grass move)
Razor Leaf
For a last move I'd pick either of these
Sunny Day
Body Slam(Or other normal alternatives)
Giga Drain
When you play against the CPU, Leech Seed is just too good because they don't switch Pokemon. So eventually whatever you use it on will faint.