So, right now what the team needs is a Talonflame check and a Stealth Rocker.
On my phone so I can't make a full nomination atm, but I'll just throw some ideas out there that can fulfill one or both of those roles and have somewhat decent synergy.
Few things that come to mind are Empoleon, Heatran, and Rotom-W.
Empoleon and heatran increases the metagross weakness but a chople berry on either could help with that.
Not really much else to work with imo, as another setup mon is really unnecessary and other stealth rockers / Talon checks don't synergize well (think chomp and lando-t).