See Full Series here: https://www.youtube.com/playlist?list=PLezAEu8shuO6qdBP5Qq_wjqRpDHhtOSDT

This is a Gym Leader episode where Metro describes exactly how he beats Crawli.
If you want to see the attempt where he wins, skip ahead to 8:20

I recognize this fight has changed a lot in recent versions, but I'll still explain my logic here.

At the time, the field was op and Air Slash could pretty much solo all the leader's Pokemon so if push comes to shove I would recommend that, but can't say if this changed in Version 6.

Otherwise, I use Delphox to wall off against his special attackers and Granbull to wall off his physical attackers where needed.

I go 1 for 1 against Volcarona with Golem who survives with sturdy and easily 1 shots it.