Since some sort of physical DD or SD/Tailwind moveset would probably be the Zard set other people used, I decided to use special Zard-X with Sun support to help set the team apart from the crowd. Max speed for other base 100s, max Special Attack for the
boom boom fire power. Dual STAB with spread, would have HP Ground but the rest of the team is built around handling Heatran, so Overheat is cool for OHKOing Aegislash and even Sassy Amoonguss without Sun support needed.
Since you obviously can't use Zard-Y on the same team, I decided to go with Sunny Day Cresselia (sorry Elegy, Ninetales just isn't that good :/). Since I wanted this to be a support set rather than CM (although you could use that if you wanted since Zard will lure Heatran for it, and can also beat most Dark types under the right conditions), I added a bunch of cool support moves. Skill Swap is actually awesome on Cress, it can Skill Swap Zard to give it Levitate (since it's special it doesn't care about Tough Claws); and regardless of which Zard Mega or moveset you use, taking Flash Fire from Heatran helps Zard to pummel through teams with Fire attacks. Using it on Intimidate and Parental Bond is also cool. Helping Hand is there to increase the output damage of the team, although you could probably use TR for opposing TR teams if you want. Psychic is obligatory STAB.
Landorus-T adds Intimidate to help out with opposing Lando, Talonflame and Diancie. I decided to go with Arctic's bulky Lando since it is a more reliable check over the course of a game. It also always lives a Sucker Punch or Knock Off from +1 LO Bisharp from full which is nice. Stone Edge is nice for power, and with "elping and cresselia" support you can OHKO even bulky Thundy-T to stop those meddling yellow mages :D.
Bulky Rotom-W provides burn support and also a much needed T-Wave immunity. Since you ideally want Sun up as much as possible, and Thunderbolt still does nice damage, I decided to swap out Hydro Pump for Snatch. Snatch is a move which steals a particular type of status move from an opponent if they use it and makes Rotom-W use it instead. The main target is things using Substitute, but it also works on setup moves i.e. CM and also recovery moves i.e. Moonlight (basically cool beans). Notably you also steal Psyche Up, Safeguard and Reflect/Light Screen, but not transform.
Talon provides fast priority, and so helps the team against faster opponents, and also helps somewhat against the pretty terrible TR matchup. SD Talon would be a cool option, but sadly we need Steel Wing so we don't completely add to the Diancie weakness. s/o to Sharp Beak for being cool to bluff banded, but sadly we need LO to get the OHKO on Naive Diancie (note: Hasty
is better though!).
Scarf Loom also adds some speed to the team, and also a fast surprise Diancie check. It also OHKOs standard Kang with Superpower which helps as well, and Spore is always a nice thing to have (also helps a bit vs TR). Adamant allows you to outspeed up to and including base 110s and Serperior, but Jolly outspeeds even lesser used stuff like non-mega Aero, Darkrai, Weavile.
