Looking at Kyurem-B, we saw that he had noticeable a Fairy-type weakness, leading us to originally choose Aegislash as his partner-in-crime. Aegislash could assist Kyurem-B in taking out those pesky Fairy-types with its STAB Flash Cannon and could also nullify an incoming Pixilate Hyper Voice from Mega-Gardevoir and Sylveon with Wide Guard.
We then proceeded to use Terrakion as the third Pokemon due to the fact he could hit hard with his dual STABs in Rock Slide and Close Combat; he was great for taking care of threats such as Talonflame, Thundurus, Heatran, Tyranitar, and Mega Charizard Y.
The next choice was a little unorthodox, but we decided to utilize Defiant Tornadus to punish Intimidaters and Icy Wind users. He took care of the team's Fighting-type weakness with the ability to resist with his Flying typing, while dealing a significant amount of damage against those Fighting-types with STAB Acrobatics. Not only that, he provided speed control with Tailwind to enable Kyurem-B and Terrakion to pull off a potential sweep late in the game.
After that, we looked over the team and saw that we had three physical attackers and only one special attacker, leading us to pick Charizard Y as our Mega Pokemon. He took care of Kyurem-B's and Terrakion's Steel-type weakness with his STAB Overheat or Heat Wave and he was a great check against Water-types such as Rotom-W with Sun + Solarbeam. I'd also like to note a STAB Overheat from Timid Mega Charizard Y in Sun OHKOs 4 HP / 0 SpD Mega Kangaskhan 100% of the time, which was helpful in several situations.
Finally, we chose Landorus-Therian as the sixth member for added coverage against Fire-types (notably Heatran), Rock-types which threatened Charizard, and Flying-types. We gave him a Scarf to outspeed the majority of the Pokemon in the Smogon Doubles metagame and he could potentially flinch the opponent with a fast Rock Slide.
We tested this team among ourselves, and we found that Aegislash didn't really possess great synergy with the other members of the team. Thus, we replaced Aegislash with Venusaur; he was a great partner with Mega Charizard Y as he could utilize his Chlorophyll ability and put threats to sleep with a fast Sleep Powder. Venusaur provided this team with extra coverage against Water-types and coverage against Fairy-types with STAB Giga Drain and Sludge Bomb. He could also switch into an incoming Water, Fairy, Fighting, or Steel-type attack if needed. Plus, the Chlorosaur combo allowed to handle Trick Room teams surprisingly well, with Charizard hitting hard with his STAB Fire-type moves and Venusaur putting TR teams to sleep.
