For hydreigon: flamethrower, Draco meteor, Acrobatics, dark pulse
For magmortar: flamethrower, thunderbolt, confuse ray/will-o-wisp, sunny day
For snorlax: body slam, crunch, zen headbutt, earthquake
For metagross: zen headbutt, ice punch, earthquake, magnet rise/trick
Thats a pretty good offensive team. Snorlax you should save for an emergency because they have some pretty good speed sweepers out there like mienshou or d-danced gyarados. Snorlax is pretty when it comes to stalling and taking a hit so use it wisely. And make sure your team has good speed natures and evs. Good luck.