" I recall that time in Unova, where I was near ban worthy under rain. Heh, I may not ma as strong now, but don’t think I’m below S tier. "
-Keldeo
Hi guys, girls, my little poney ambassador and anything in-between! Nope, I am not letting you vote this time. I might be squeezed between two dissertations for school, but I was missing those very long analysis because the Pokémon was just so strong and versatile that it was impossible to summarize. I know FOR A FACT that you wouldn’t have wanted to see this one win the vote, but hear me out: this one is in the top 2 of the strongest Pokémon in Ins. OU PERIOD.
" BuT pEtEr! ThIs OnE iS nOt EvEn A dElTa Or A nEw PoKéMoN! " I hear you typing since I have good hears. But let me ask you, was GSC Snorlax a new Pokémon? No, it wasn’t. True, you might have stronger Pokémon in Mega Feraligatr, Mega Typhlosion and Mega Miloctic, but they are no match for one thing they don’t have. You want to know what? In that case, let’s start, shall we?
Be warned, since there is no competitive usage stats avaliable, I do not have any reliable ways to accurately predict the metagame. This analysis is theoretical and does not entirely reflect a Pokémon’s viability.
Typing, Stats, Abilities & Movepool
Water/Fighting
Ability: Justified
Hp: 91
Atk: 72
Def: 90
SpA: 120
SpD: 90
Spe: 108
Good typing and solid stats inducing a good bulk, solid special attack and very good speed makes it a fantastic Balance Breaker. As you know at this point, base 100 is a very crowed speed tier and Kedleo outspeed all of those. Sure, it may not seems that way at the first glance, but you have to respect this MLP reject.
No, its ability is useless. True, it has shallow coverage as Icy Wind is its most decent coverage. And yes, it has solid checks. What is the problem then?
The problem
- New Moon
The increase of Dark Types in OU due to the New Moon makes fighting types stronger and especially those who can handle the extremely dangerous Bisharp. Not only Keldeo is on of the best fighting types out there, it is vey happy to also abuse New Moon itself! Now, a Choice Specs Surf booked by New Moon does damages comparable to those of rain. And as a check to most Dark Types, it could fit into literally any decently build New Moon team.
- Non Mega
THIS is SUPER IMPORTANT in its ubiquity. It is a very powerful Pokémon that can fit into ANY team, even if using a mega. Plus, many strong Pokémon fit incredibly well with almost any top tier and mid tier, making it a swiss knife at the level of Landorus-T. Its so easy to slap on a team that you MUST be somehow prepared to it.
- Typing
You know that Armored Tyranitar is just busted and super Bulky? Yeah, not anymore. Keldeo is the absolute best Tyranitar counter and does not give a 
about Tyranitar’s armour and just slice through it no matter the bulk investment. What is one of the bulkiest support Pokémon is just another victim. Water and Fighting also allow it to cover many popular threats, including Delta Arcanine,Typhlosion, Volcarona, Heatran, Mega Delta Lucario, Bisharp and Delta Registeel to name few.
- Secret Sword
Although it is minor compared to the previously mentioned one, Secret Sword is a fighting special attack that does physical damage. You know, a special attacker that can shatter Chansey and special walls. Oh yeah, is also allow it to destroy Armoured Delta Volcarona. You know, another special sponge and wall to many special attacker. It is also a water type that is not stopped by Ferothorn.
Sets Suggestions
Choice Specs
Keldeo @ Choice Specs
Ability: Justified
EVs: 252 SpA / 4 SpD / 252 Spe
IVs: 0 Atk
Timid Nature
- Scald / Surf
- Secret Sword
- Hydro Pump / Surf
- Icy Wind / Focus Blast
Probably its best and most strait forward set. When using (or facing) a New Moon team, I recomend to drop either its ability to burn its checks or Hydro Pump to take advantage of the weather. While it seems counter intuitive, Focus Blast is stronger than Secret Sword by a great margin, it notably 2HKO Assault Vest Tangrowth and OHKO Rotom-W after Stealth Rock. Hidden Power Electric is also good coverage option to deal with Starmie and Gyarados. Icy Wind is preferred over Hidden Power Ice due to the speed drop.
Choice Scarf
Keldeo @ Choice Scarf
Ability: Justified
EVs: 252 SpA / 4 SpD / 252 Spe
IVs: 0 Atk
Timid Nature
- Scald / Surf
- Hydro Pump / Surf
- Secret Sword
- Icy Wind / Hidden Power [Electric]
The sets might look similar, they actually serves very different purpose. While Choice Specs goal is to wallbreak, this Keldeo set is a Revenge Killer and a Sweeper. On top of it, this Keldeo set allow to outspeed and revenge kill Adamant Mega Swampert! It is also faster than most Choice Scarf users like Landorus-T, Garchomp, Hoopa-U, Kuyrem-B and Delta Darmanitan.
Sub CM
Keldeo @ Leftovers
Ability: Justified
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
- Substitute
- Calm Mind
- Scald
- Secret Sword
This set allows to take advantage of bulkyer Pokémon that tends to use status against it like Amoongus and Support Tyranitar. Moreover, this set is incredibly strong against Stall teams. Think of it, Unnaware Clefable is pretty much the only common stall Pokémon that can try to annoy it. Outside of the stall matchup, most hearten variant has no mean to pass this Pokémon. And given how good Heatran is, that is a great selling point.
Other options
Hidden Power Flying allow to pass Mega Venusaur, Delta Tangrowth and Amoongus, but has little use otherwise. Offensive Calm Mind is also a think, but setting up is dangerous. Taunt is also a viable option. If you are very concerned about bisharp, Rest Talk is possible to keep Keldeo healthy a maximum.
Good Teammates
- Delta Registeel set up molten rocks that dissuade any Grass types from coming safely.
- Other Fire types also like Keldeo ability to deal with Chansey for the special ones and opposing fire.
- Mega Metagross for an outstanding wall breaking core with Keldeo as they cover each other’s check and have amazing synergy. Keldeo cover Bisharp and Mega Scizor to name few and Mega Metagros cover… almost anything else.
- Weather setter as Delta Serperior and Spiritomb are amazing partner because they set-up weather in which Keldeo thrive with. Our little unicorn also fit well with most team members like Bisharp and Delta Dragonite.
- Latios is very good with Keldeo, as they also cover each other’s check and counter.
- Listen, its just too long to tell every notable teammate. Smogon had to do 2 text paragraph on every set to list potential teammate so just… pffff…
Checks and Counter
- Bulky Grass types are difficult for Keldeo to bypass, mostly Amoonguss, Celebi and Mega Venusaur.
- Psychic Types and especially those who resists water, are problems to Keldeo. Latios and Mega Alakasam are notable ones,
- Bulky Waters like Suicune and Slowbro are near impossible to get over. Mega Miloctic in particular don’t care about any coverage option, revenge kill it and can chip it down thanks to its ability.
- Fairy Types in Mega Altaria, Azumarill and Clefable are very dangerous to Keldeo. Most of them have good special defence and resists Fighting.
- Electric types are also problematic for obvious reasons.
- Select Dry Skin users in Toxicroak and Delta Tangrowth are good checks to Keldeo as they are immune to Water and take little from Secret Sword.
- Mega Delta Charizard can eat an Icy Wind in a pinch and OHKO back. If Keldeo is choice locked on Scald or Secret Sword, its the jackpot.
- Shedinja is… a troll… but it still walls it.
Overall
I think Keldeo is the next Landorus-T. I mean it will be used almost everywhere from rain to new moon, as well as Balanced, Bulky Offense and Offense. Seriously, it just looks SO GOOD in the metagame I would be extremely surprised if it is not on the top 5 of usage.
- Mega Delta Venusaur
- Latios
- Mega Gardevoir
- Armored Tyranitar
- Landorus-T
- Other