I was looking through this a bit, and I noticed you provide a bit
too many examples compared to most other analyses. Some of them are really shaky imo and aren't too necessary.
Most of its usual counters in Celebi, Tentacruel, Latias, Latios,
Hm? Sure, you can hit him with Icy Wind, but what else? If it has Specs, Latios easily OHKOs Keldeo with Psyshock, Thunderbolt, or a Draco Meteor. If it has a Scarf, it 2HKOs with all these moves, and Icy Wind doesn't help because you can't OHKO it with anything unless you predict the switch, use Icy Wind, and then follow it up with another Icy Wind, a feat that could be accoplished with Specs just as easily. You need to use Hidden Power Bug to secure the 2HKO, which can be an issue.
A calc to prove that this is nowhere close to the KO you need
252 SpAtk Expert Belt Keldeo Icy Wind vs 0 HP/0 SpDef Latios: 44.52% - 52.49% (2-3 hits to KO)
Against Latias you are doing pathetic damage. Assuming its offensive, its still avoiding the 2HKO thanks to that Special Defense and it ends up similar to specs Latios - dead.
252 SpAtk Expert Belt Keldeo Icy Wind vs 252 HP/0 SpDef Latias: 31.59% - 37.36% (4 hits to KO)
Toxicroak, Jellicent, and Amoonguss can easily be flattened with the aid of its new Expert Belt.
You can't hit Toxicroak for more than 40% damage with your best move against it, Hidden Power Electric (if it has absolutely no investment in defenses). Toxicroak in return 2HKOs you with a Life Orb Drain Punch and recovers enough HP (especially in the Rain) to make it as if Keldeo wasn't even there in the first place.
Keldeo is destroyed by Amoonguss. It can't do anything to it and Keldeo gets 2HKOed with Giga Drain (which means Amoongus just heals itself)
252 SpAtk Expert Belt Keldeo Icy Wind vs 252 HP/228 SpDef Amoonguss (+SpDef) : 28.24% - 33.8% (
4-5 hits to KO)
28 SpAtk Amoonguss Giga Drain vs 0 HP/0 SpDef Keldeo: 50.15% - 59.44% (2 hits to KO)
It should be noted that Expert Belt Keldeo can also lure in Pokemon trying to resist one of its STABs or coverage moves (very common if they predict the choice set) such as Dragon Dance Dragonite, Dragon Dance Gyarados, Rock Polish Landorus-I, Rock Polish Landorus-T, Dragon Dance Landorus-I,
This is mostly a personal thing, but why is the specific set invluded? It really seems like ANY Dragonite could expect the Choice set, whether it be the Choice Band, the Dragon Dancer, the Hurricane spammer, etc., and same with Gyarados. Including two (three?) Landorouses seem incredibly redundant - if it counters one, it should likely counter the other one easily
Landorous also doesn't learn Dragon Dance.
opposing Keldeo, Terrakion
A Pokemon that is weak to both STABs would never even think about switching in, even if it has a coverage move incoming. In my experience, 90% of the time a Keldeo is going to use Hydro Pump, Surf, or Secret Sword, and if it relies on a coverage move to take out the foe, it usually doesn't go in the battle and do it. Terrakion isn't really needed imo.
LO Lati@s, Nasty Plot Celebi, Growth Venusaur, Swords Dance Scizor, Forretress, Hippowdon, and Politoed.
Forretress isn't a counter - it hits far too weak and can't do anything back to Keldeo. It also takes a considerable amount of damage from both STABs, and all it can really do is set up hazards... which isn't very much. And, as mentioned, Keldeo with a Choice set will usually be using a STAB move, so Forretress probably won't switch in.
Venusaur gets hit hard... that is true, but Keldeo has no buisness even attempting to take it on. A Life Orb Giga Drain OHKOs just too often - around 30% of the time with a Timid Nature and all but 6.25% of the time with a Modest Nature (Modest Venusaur is more threatened by Scarf Keldeo because its faster.
Politoed seems sort of like an afterthought if anything, but I personally wouldn't switch in Politoed considering it powers up Hydro Pumps, which in turn could do incredible damage if backed up by a boosting item like Specs (which the opponent may believe that you have). Secret Sword isn't exactly kindly either, and Politoed can't do much back to it.
Finally, this is pretty minor, but try not to abbreviate Lati@s in analyses. Also, as aforementioned, the chances of taking a hit from LO Latios is slim, and Latias will usually come out on tip,
In AC, I don't see how Breloom deals with Thundurus-T at all, or why taking out Feraligatr is necesary (its rare and can't do anything back to it that is threatening). Breloom can only do 40% with Mach Punch at best to Thundy-T while it gets OHKOed easily by Hidden Power Ice. Also, []s are not needed around the Hidden Power types, so remove those.
You don't need to implement all this but this is just for thought I guess