>>16689239Heatran is a great SR lead. It also has fairly good offensive synergy with Garchomp. Mamoswine, Landorus-T, Jirachi and even Garchomp itself are some other good SR users for bulky offense teams.
Garchomp likes offensive partners that can help it break through Pokemon like Skarmory, Hippowdon and Ferrothorn. One way to do this is using special attackers with good matchups against (most of) them like Heatran, Keldeo or Rotom-W. Alternatively you can just wear them down by stacking physical attackers. Think along the lines of CB Terrakion or dragon spam.
Mega Venusaur is viable.