you have a LOT of ground weaknesses in this team; that is going to hurt you severely, especially in doubles/triples
Gallade is also very slow for what it does and lacks multi-target moves to round out your doubles/triples; consider replacing him or adding a tailwind/baton passer to speed him up
you have pretty much nothing defensive; while dedicated walls are bad in doubles and triples, your lack of effective walls makes you susceptible to set-up sweepers, since Armaldo doesn't have Sturdy. You need something that can effectively tank and either phaze or KO enemy attackers. Cloyster needs setup to do so, making it a poor choice for this task.
Typically, you scarf your revenge killer, since Hydreigon has decent but not great speed. That 98 speed leaves it slower than most offensive threats, so you'll need at least a Timid nature if not a scarf for the role you intend.