Shedinja always dies to Iron Barbs Ferrothorn when Shadow Sneak or X-Scissors is used so that must be mentioned, considering Ferrothorn is so common.
Venusaur sort of went extinct. Absorbing Toxic Spikes is its main advantage over other sweepers. The Mixed Growth set looks iffy to me. Sleep Powder is like Venusaur's most important move as it gives Venusaur a chance to set up. Setting up on Ferrothorn is always nice.
Dialga - Mixed Dialga should still use Max Attack / SpA to take out Chansey. Otherwise, it is not performing its niche which is element of surprise. Functions best with Trick Room. Max HP Dialga should just use max SpA and four Special Attacking moves or Stealth Rock with 3 attacks. Something like Thunder, Fire Blast, Draco Meteor and Stealth Rock/Aura Sphere.
Ferrothorn - Besides teammates, drop Gyro Ball to AC and move Power Whip as the main move. Hitting the weather Ubers is that important, has more PP and does more damage to things like Palkia and Blissey. Drop Stealth Rock and put it in AC, Spikes is the main reason to use Ferrothorn. Leech Seed should be a main move, as Ferro needs it for recovery and annoyance. Also why not just max out SpD, it maximizes you chances to live through Fire Blast in the rain from Specs Dialga? Attack EVs hardly helps anyway and
Sub Dark Arceus is outclassed by Refresh.
Heracross - Heracross is still the best Darkrai counter in existence. If Gastrodon is approved, then why not this bug? Unlike Gastrodon, Heracross has STAB Megahorn which is an 85% OHKO on all Mewtwo variants. Sleep Talk + Guts is very useful. Close Combat OHKOes most Steel-types such as Ferrothorn and it isn't weak to Power Whip or Focus Blast, unlike Terrakion.
Kyogre- I will put Max SpA and HP for this set. Chesto Berry means Kyogre should attempt to sweep as fast as possible. Extra physical bulk doesn't really help much here. More bulk means you should just use the mono attacker.
Lucario - I believe Jibaku agreed Lucario shoud be dropped. It doesn't do much. Terrakion outclasses it in sweeping. It's ExtremeSpeed isn't very strong either and it depends too much on hazards to sweep well. With V-Create Rayquaza and Arceus on the rise, I don't think Lucario is viable.
Mew - Don't like this. It is too unreliable, not bulky, weak ass. Unpredictable isn't enough anyway, Mew isn't going to sweep you like Mewtwo and not as bulky as most Ubers.
Palkia - Specially Based Mix sucks because you won't get past Chansey anyway. I think change it to Lustrous Orb Special. Surf, Spacial Rend, Fire Blast and Thunder are staples already. Aqua Tail or Outrage doesn't really do much this days and it makes you Arceus setup bait if you are stuck on Outrage.
Qwilfish - Maybe just merge Support with Sweeper. Spikes can go in over Destiny Bond.
Skarmory - Probably needs more mention of Spikes and how Skarmory owns any common SD Arceus variant.
Terrakion - Tyranitar doesn't counter Lugia or Giratina. Both have some ways to deal with Tyranitar, Will-O-Wisp or Reflect. Tyranitar will sadly be stalled out. Scarf Tyranitar is too weak to get past them. Excadrill seems like a good choice to weaken Groudon or Lugia/Giratina.
Ho-Oh's EV spread for the Tank set should be 248 HP / 176 Atk / 84 SpD in my opinion. It makes sure Ho-Oh doesn't die to 2 hits from Scarf Palkia's Thunder. Less Attack doesn't lose any KOs. Whirlwind is a good option, I like it to thrash opposing stall teams particularly those with Giratina. Leftovers should be the preferred item to me. Life Orb makes Ho-Oh dies fast and you might as well use the Offensive set with it.
Groudon analysis seems fine to me. Might want to mention a more Offensive support Groudon set though. More mention on Fire Punch to OHKO Ferrothorn and Forretress. Fire Blast takes out any Skarmory in 2 hits, makes Groudon set up bait to Ho-Oh unfortunately.
For Giratina-O, I think a Calm Mind set with Rest and Sleep Talk should be included. The Mixed attacker set should change slashes in the last slot. It should be Hidden Power Fire / Thunder. Earthquake is rarely used, only against Heatran and maybe Jirachi or Steel Arceus. Will-O-Wisp is useful for crippling Ferrothorn in the rain but is useless otherwise. Defensive set using Will-O-Wisp is better off with Giratina.