Hey,
Analytic just a few nitpicks.
You could have tried Special Defensive Skarmory over Manaphy (Eh, I wouldn't say Sdef Mana checks Landorus, Scald does not ohko, while Earth Power is a 3hko, mana has troubles coming in, then again, what actually stops Landorus), it gives the team a steel resist that doesn't die from Superpower like Heatran and a defogger, while at the same time helps against Mega Diancie and opposing Mega Gardevoir (since you also changed Victini to Heatran, who dies to Focus Blast), oh, it also helps thanks to Counter against Mega Metagross, who has many opportunities to come in here, especially since Vicitni checks non-eq versions.
Victini in that team acted as a stallbreaker, as such I agree that Heatran would be a better fit (after changing Empoleon) but i don't think that changing Rock Slide would be the way to go with Landorus, Stallbreaker Talonflame totally destroys Heatran sadly, and manaphy cannot come in after a swords dance boost, also, scald fails to 2hko if leftovers, otherwise if no item with Acro, Scald has a very low 8.6 chance to 2hko, Rock Slide also helped the team against Mandibuzz, and; most importantly, a lure for Tornadus-Therian, which is troublesome, especially versions with Focus Blast/Superpower that can trouble Heatran.
I would have also considered to give Thundurus 76 atk evs, this way Latios would have been ohkoed 100% of times after Stealth Rocks support.
Other than that, great stuff (consider using the Hide function when posting calcs), keep up the good work!