I actually have used Lanturn before, it's good against rain but with no recovery at all, it's not very good outside of rain where usually Gastrodon can do the same thing outside of rain, but better, due to recovery, and generally higher stats (especially offense).
You're right, both don't like sun team very much, but are you really saying that Lanturn would do well against a Sandstorm team?
No, I'm not saying that Lanturn excels against Sandstorm teams, and I have no clue how you got that out of my post. I'm saying that Gastrodon doesn't do much better. Gastrodon still can't switch into CB Terrakion Stone Edge (it gets 3HKOed, and it can't even 2HKO Terrakion back). Gastrodon still isn't going to handle that SD Lucario your opponent has. And Gastrodon still says "Fuck." when a Celebi switches into it. My point is, Gastrodon is no better off against a Sandstorm team than Lanturn is.
And stop saying Lanturn has no recovery. It heals every time it comes into the STAB of Jolteon, or Magnezone, or Rotom-W, or Thundurus-T, and more (all of which it counters anyway). And the number of Pokemon that love running Thunderbolt for coverage isn't that small either.
If you want to outspeed Gliscor that's going to take quite a few EVs (in fact you would need a Speed boosting nature to achieve this), and with that you're losing out on either Special defense, so that Earth Power from Heatran has a chance to 2HKO you, or from Special attack, to which point you won't be hitting as nearly has hard as Gastrodon would. So, Would I use that much speed, and hinder my offensive or defensive capabilities with Lanturn just to out speed Gliscor for fear of an Earthquake, when I could just use Gastrodon or even Rotom-W to achieve the same thing but without losing offensive and defensive capabilities?
I never said it was a good idea to out-speed Gliscor. I said that Lanturn could do it, because you made it seem like out-speeding Gliscor was a big deal (not like Gastrodon can out-speed Gliscor). Gliscor still gets fucked if it tries to switch into Lanturn. Oh, and by the way, Lanturn can tank an Earthquake from full health, and OHKO back. So Gliscor is actually shit against Lanturn.
How does Gastrodon fare against Gliscor? Well, it gets 2HKOed by a completely uninvested +2 Earthquake. Meanwhile, Scald fails to KO Gliscor in return. A Gliscor with 252 Atk EVs (and a neutral nature) will OHKO Gastrodon with a +2 Earthquake after Stealth Rock or Spikes (and without any HP investment, Gliscor STILL isn't KOed by Scald). So Gastrodon does shit vs any Gliscor with SD. And don't get me started on what SubToxic Gliscor does.
So you don't need to detract from SpDef EVs, and Heatran actually can't 2HKO you with Earth Power. Lanturn is almost as bulky as Gastrodon, and is more powerful than Gastrodon. As I've been showing you, Gastrodon is better than Lanturn in NONE of the ways that you've said.
And what the hell was that about Rotom-W doing the same thing? Rotom-W is hardly bulky at all, and gets ass-raped if it tries to tank a Thunder from Thundurus-T, or anything like that. Rotom-W also can't Ice Beam the pants off a Breloom which comes in to set up on it.
That pretty much sums of Lanturn right there. It needs to make too many compromises to be effective. Yes, it can be good in rain but if you are facing Sandstorm or even Weatherless it won't be as good as Gastrodon.
Okay, well I don't what exactly your experience with Lanturn was, but it's sorta clear that you weren't using it right. Lanturn doesn't need to make many compromises at all, and I've shown that Gastrodon fares just as, if not more poorly, in all the situations you outlined. No, I'm not calling Lanturn the end-all be-all of OU nowadays, but you need to stop saying its outclassed by a Pokemon that can't even do Lanturn's job.
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OKAY, so about WATER PONY. I would agree with everyone who's said that SubCM and Specs Keldeo are generally gonna be what Keldeo runs. They do most all of what you would expect Keldeo to do. And they're good at it (Water Pony fucking terrifies me). But CM + 3 Attacks is also notable, as ArcticBlast said. It's harder to use, from what I've seen, than the other sets, but it's the scariest of all if you get it just right, because the freedom to switch moves, and extra coverage, makes it about impossible to wall after a boost (although it's more easily revenge-killed than any other set). Dang, I love Water Pony, because it's the second cutest Pokemon of all.
Oh, and Scarf Keldeo does work, but only by virtue of its stats. Just about anything with 108 Speed and a 129 Attack/Special Attack could run a viable Scarf set. But honestly, why would you run Scarf Keldeo when Scarf Terrakion exists? Terrakion's movepool is MUCH better suited to revenge-killing than Keldeo's. Things like Salamence, Gyarados, and even Venusaur don't feel particularly threatened when a Scarf Keldeo comes in, but they all piss their pants when a Scarf Terrakion finds his way in.
Also, I've seen so many battles where someone thinks that resisting Keldeo's STABs makes something a counter. It doesn't. Shit like Dragonite gets 2HKOed in the Rain, and yet people never seem to learn. It amuses me.