Give Yanmega the item "throat spray" Throat spray makes sound base moves more powerful. Then have have Yanmega learn bug buzz (which is a sound based move)

Make sure Yanmega has the ability "Speed boost".

Speed boost makes it faster after every turn

Then give it a Ground Tera type. Which makes it less weak to fire or rock.

That's it. You'll be sweeping teams with Yanmega in no time.

Make sure to activate Tera in the begging of battle though (depending on situation)

Yanmega will basically go first EVERY FRICKEN TURN!

Lol

Who's knows? Maybe it could be used for....other things....