SCIZOR-MEGA - While your EV layout used to be viable last season, times change and now a better EV layout would be 252 HP/248 Def/8 SpD to tank hits better. Although U-Turn is completely viable and offers Bug STAB, my main problem with it is that when you use it you lose all your attack boosts from Swords Dance. Instead, use Knock Off to cripple tanks. Also, not that it matters that much, but make Mega Scizor's pre-mega ability Light Metal to tank Grass Knot and Low Kick better. Not very common in OU, but Scizor always mega evolves immediately before attacking anyways, so it doesn't have any negative impact on Mega Scizor. Another benefit is that it stops Ditto from copying you and also having Technician.
HEATRAN - Your Heatran is completely fine, and its ability has incredible synergies with Mega Scizor, which is 4x weak to Fire Types. My only adjustment to make is to replace Heatran's 4 Special Defense EVs for 4 Special Attack EVs to boost its Magma Storm further when Heatran (hopefully) gets a Flash Fire off. Its nickname doesn't really matter because if your opponent sees a Mega Scizor and a Heatran on the same team, they'll definitely assume it has Flash Fire anyways.
LANDORUS-T - The Leftovers recovery for Landorus-T isn't very useful because the set you're running generally just sets up Stealth Rocks, maybe pulls off a few Earthquakes and then U-Turns away. Instead, use a Rocky Helmet to punish physical attackers. (Most people don't expect a defensive Rocky Helmet Landorus-T, so they'll try to use a physical move on you anyways, which really helps this set a lot.) Your team is fairly easily swept by Zygarde. Change this by making Landorus-T's EV layout 252 HP/144 Spe/112 Def. 144 Speed is to outspend and shut down Heatran. Here:
0- SpA Landorus-Therian Hidden Power Ice vs. 4 HP / 0 SpD Zygarde: 172-204 (48 - 56.9%) -- 84.4% chance to 2HKO
252+ Atk Zygarde Outrage vs. 252 HP / 112+ Def Landorus-Therian: 159-187 (41.6 - 48.9%) -- guaranteed 3HKO
252+ Atk Zygarde Devastating Drake (190 BP) vs. 252 HP / 112+ Def Landorus-Therian: 250-295 (65.4 - 77.2%) -- guaranteed 2HKO
Even if Zygarde gets a Dragon Dance up, it'll just be neutral due to Landorus-T's ability, Intimidate. For some reason, damage calculator doesn't have an option for Rocky Helmet as an item, but Rocky Helmet damage is 1/6th of the attacker's health. The standard Zygarde has 358 HP, so Rocky Helmet will do about 59.6666666667 damage. (16.6666%) In other words, no matter what, in this scenario against Zygarde (the most common one), Landorus-T will ALWAYS 2HKO when you factor in the Rocky Helmet if you choose this EV layout.
KELDEO-RESOLUTE - This set is 100% smogon approved and maximizes Keldeo's potential.
ZAPDOS - You aren't making use of Zapdos's stellar speed stat. Fix this by making its EV layout 252 Spe/248 HP/8 Def with a Timid Nature. You don't really need Defog. Instead, use Hidden Power [Ice] to shut down the ever so common Landorus-T. Replace Zapdos's ability Pressure with Static to punish physical attackers. The chance for your opponent to get paralyzed is further increased by Discharge. Because every pokemon in PS is maxed PP, pressure isn't nearly as useful as Static.
CHANSEY - 252 in both defenses is only useful in BSS because in that format you need Chansey to be bulky in both defenses. However, in OU, or any other format that isn't BSS, it's always best to run max HP to boost Chansey's monstrous HP stat and so that Chansey can tank physical hits better, which is a necessity in OU. Keeping this in mind, try the smogon suggested EV spread, 252 Def/244 HP/12 SpD. None of your pokemon are particularly crippled by status ailments, so replace Heal Bell with Stealth Rock in case your Landorus-T faints. (Probably due to an Ice Beam.)
