This post might be a little controversial as I see it, and I expect a lot of good discussion coming out of it.
Extremekiller Arceus is still on unparalleled level amongst the members of this tier and there are three reasons I will outline in this post. First off I don't give two shits about the "criteria for S-rank" since these are bias towards versatile mons like gen5 Dialga, aka mons that can do a lot of things okay but doesn't have a role that it is "best at." If a mon has one thing going for it and it is so good at it, it doesn't really matter whether it can run other sets (see gen5 Genesect). For Extremekiller Arceus, this stands true, because it obviously has only one set going for it- this set however excels on an entirely different level than that of any Pokémon in the game. Why is it so needed that a Pokémon should beat both offensive and defensive capabilities? Why must a Pokémon in S-rank be able to fulfill different roes if it fills one role to such excellence?
The only thing a S-ranked Pokémon needs in my eyes are:
- Either massive, unmatched defensive OR offensive qualities, or in some cases they have both.
- Capable of fulfilling multiple roles on defensive or offensive ends, both ends or simply fulfilling one role at either end that it fulfills to almost absolute perfection.
- Require no support.
- Have immense utility to offer.
There is absolutely no logical reason to ever demand Pokémon to fulfill multiple, both offensive and defensive roles when such a Pokémon have one role if fulfills in such a way that even the factor of surprise will not matter. Onto my three reasons on why Extremekiller Arceus belongs to the highest rank there is.
Many of its old checks and counters have diminished in value, stressing teambuilding to the point where it actually has less viable check and counters than it had before.
Yes, this is true and I think we can all agree on that the following: Terrakion, Skarmory, Ferrothorn, Excadrill (sand rush), Forretress, Kabutops, Omastar, Arceus-Fighting, Genesect, Giratina-O (and A for that matter) and Arceus-Ghost were in some way or another able to either counter, revenge-kill or soft-check Arceus-Normal. All these have one thing in common- they are all worse than they were in BW. Exceptions can be made, however, and there are some teams where Choice Scarf Terrakion still fits on, there are some uses of Ferrothorn and Giratina-O but in general these checks were better off before the transition into the XY metagame.
Also, do note that some of these mons, like Genesect could only revenge-kill a weakened Arceus while at the same time being very healthy itself, but my bottom line still stands through- a healthy Genesect was a roadblock towards your sweep.
What did emerge in this generation as in means of handling Extremekiller? Defensive Yveltal, Mega Scizor, Kangaskhan as well as Gengar deserves a mention. Defensive Yveltal still loses as it switches in, but in the same vein Arceus-Fighting was a good check last generation, Yveltal is in this generation. Scizor has some trouble taking Life Orbed Earthquakes and can obviously get wrecked by the rare Fire move, but is otherwise a fine check. Kangaskhan can chip off damage with Fake Out, and can with sacrifices of other team members be a quite okay emergency way of handling it, although not a way that should be relied upon. Lastly, Gengar can when mega-evolved outspeed even Jolly variants and Destiny Bond you down- this is never going to be a consistent method as it requires both a sacrifice and the fact that Gengar must be mega evolved already. Lugia is a check that have arguably gotten better in the transition, and I really can't argue against that except for the fact that it is Taunt-weak which makes it very manageable for your teammates. Even if this is an evidence of support need, a Taunt-user fits nicely on most teams anyway, not in the same vein that Stealth Rock is a must on any team, but still. Speaking of Stealth Rock, that is obviously another way for Extremekiller to get past Lugia somehow.
Lastly, even though Will-o-wisp using Arceus-Formes are more popular this generation mainly due to the accuracy buff on this move, these aren't consistent methods any player should use as their stand alone method of checking Extremekiller, since Normal-resisting formes like Steel and Rock fall to a Jolly Life Orb Earthquake at +2 as well as Lum Berry variants- while the formes that doesn't resist Extremespeed will more than likely fall even though they manage to burn it (as well as the fact that pushing these formes into +2 Extremespeed range is easier, and that Lum Berry Arceus still beats these). As with this, I conclude that Arceus-Normal has fewer checks than it used to have.
Extremekiller Arceus has to contend with less opportunity cost in this generation
While people usually see the opposite in this case, this is nothing but a false fact. Support Arceus with Defog are viable, yes, but they aren't needed on any teams without hilariously hazard weak mons, like Ho-oh and Lugia. Because of the buffed Defog, not many teams do in fact deploy old spike-stacking strategies. Even stall teams finds themselves more reliant on status than entry hazards to get needed chip damage to win games. Another important notion here is: if Gen 5 Ubers was more hazard centric, then why did many successful teams not have countermeasures to entry hazards? The answer here is rhetoric- many teams were built so they didn't have a big weakness to hazard based strategies and the members on those teams were picked because they were excellent at taking advantage of the free turns hazard setting gave them, as well as their good ability to deal with hazard setters in what would be a more proactive way. A Defog Arceus is passive at removing hazards- for more offensive teams these proactive ways to deal with opposing hazard setters are still good, even in XY. With most teams only carrying Stealth Rock as their entry hazard of choice, dealing with entry hazards is maybe even less needed?
Was there more opportunity cost using Extremekiller-Arceus last generation? Yes, with Arceus-Ghost in S-rank and Arceus-Fighting being really good, even I as an avid user of it always considered the cost of not using support Fightceus or CM Ghostceus. As it turned out, the two teams I found best out of my hand-made teams in the previous generation had a CM Arceus-Ghost and a support Fightceus, respectively.
This generation is different. Arceus-Ghost's utility as a spinblocker and sweeper is diminished. Its SD set isn't nearly as good as some people think it is- the lack of strong priority hurts it (see my next point) and Arceus-Fighting is a mon we shouldn't even focus too much on in this generation, which is sad.
The opportunity cost instead comes from Defog Arceus, but as I outlined earlier, only teams with a clear need of having hazards off their field will need a Defog-user. Since Defog removes hazards from both sides of the field it may be good for you to actually get your Stealth Rock up to pressure these kinds of teams (I'm mainly talking Ho-oh based ones btw) to using Defog, giving you free turns. Unless you absolutely need it, you can most likely force your opponent to waste turns using Defog while you really won't care if there is SR on both sides of the field. This is why you can never claim that you are giving up the opportunity to use Defog Arceus when you have opted for Extremekiller Arceus, unless your team in fact desperately need this support, and not nearly as many teams do in fact need it, as opposed to what many people think.
Typing wise, yes, Extremekiller isn't providing much synergy but you provide offensive synergy and revenge killing ability on many types of teams. Your offensive presence makes your opponent very wary of letting of his/her means to stop it before it has revealed itself, but more about its actual qualities in my next point.
Extremekiller Arceus is the best revenge-killer in the game- and in extension it is a check to nearly every sweeper in existence
Outside its sweeping capabilities , which I in fact never even mentioned (I mentioned how it has checks, not how easy it is to sweep late game) Arceus-Normal is the best revenge killer in the game. There is no surprise that in the CC section of the usage stats, this Pokémon is far more represented that anything in the game. If you can't OHKO what you want to pick off, you can sometimes (most of the time) nab a SD and countersweep. This immense utility along with its offensive presence more than makes up for the lack of a Defog Arceus on many teams. Especially useful is its ability to pick of Mega-Blaziken at around 60-70 %, something really valuable for all teams. In my eyes, only Kangaskhan is close to Extremekiller Arceus's level of revenge killing fast sweepers.
Now release the kraken
