I think as we can all tell, the original discussion choice in the OP referring to
Ice Beam Keldeo was quickly deemed to be very, very good. Not only does it remove its counters from play with the use of a Hidden Power, but it also gives him high powered coverage on non-Choiced sets that allows him to hit checks such as Celebi, CM Latias, and others extremely hard. It would go down to Jellicent or Tentacruel to combat him, but even then the user still has the option of a Hidden Power to hit both very hard (Electric hits both, but hits Jelli harder, iirc. Psychic hits Tenta harder, I think, but not as much with Jelli). All in all, I think the gallery has come up with the conclusion that Ice Beam Keldeo may be a little too good for this metagame, if not completely broken according to a few's arguments on the matter.
So, I suggest we funnel in on another topic so the comments and discussion are more centralized, allowing for more focused and in-depth arguments on the Pokémon at hand. I'm not saying that all of the ideas being ushered into this thread are bad or unwelcomed by any means, but I suggest that we should go one at a time, so there's healthy conversation instead of multiple, not so healthy conversations that have one comment and then are forgotten.
So, I think we should talk about a Pokémon that doesn't see much use in the OU tier, but can do serious work with its good typing, great stats, and wide movepool (in both attacking and support):
Cobalion
Now, as we all may know, Cobalion's speed and monstrous Defense stat, as well as access to Taunt, Stealth Rock, Thunder Wave, and Volt Switch make it a great utility Pokémon in OU. One of its only downsides is its very weak Special Defense stat, sitting at 72. While its offensive sets have great coverage and pack decent power, Cobalion seems to still get pushed away due to Lucario sharing the same typing and better offensive stats. This makes Cobalion mostly outclassed as an attacker. Another unfortunate downside of Cobalion's is that one of his most exploitable weaknesses, that in Fire-, makes him near dead weight on Sun teams, as most things like to outspeed it and fire off HP Fire and Fire Blasts, aimed at its very weak Special Defense. How can this problem be remedied?
What if Cobalion received Heatproof from the Dream World?
Heatproof, as we all know, is an ability that acts as a buffer against Fire-Type attacks. Said Fire-Type attacks are Cobalion's worst nightmare, but now they can be properly dealt with due to its new ability. Some calcs for reference on Cobalion's new ability helping it out in sticky situations involving threatening Pokémon like Venusaur and HP Fire Latias:
252 SpA Life Orb Latias Hidden Power Fire vs. 252 HP / 0 SpD Cobalion in sun: 351-413 (90.93 - 106.99%) --
43.75% chance to OHKO
As we can see, Cobalion is absolutely raped by HP Fire in sun by the ever common Latias. But, let's take a look at how he fares with his new ability:
252 SpA Life Orb Latias Hidden Power Fire vs. 252 HP / 0 SpD Heatproof Cobalion in sun: 177-211 (45.85 - 54.66%) --
26.17% chance to 2HKO after Stealth Rock
As we can see, Timid Latias can only attempt to 2HKO Heatproof Cobalion in the sun with HP Fire. Also note that this is
without any Special Defense investment on Cobalion. Let's see some investment come into play:
252 SpA Life Orb Latias Hidden Power Fire vs. 252 HP / 48 SpD Heatproof Cobalion in sun: 164-195 (42.48 - 50.51%) --
guaranteed 3HKO after Stealth Rock
With only some investment in Special Defense, Cobalion comfortably takes at least 3 Hidden Power Fires from Latias in the sun. Not only is this a fantastic change from before, but it means that Cobalion can afford to run a Speed boosting nature over a SpDef boosting nature in order to help outspeed certain threats.
Now we move onto Venusaur, who is an absolute nuke in the sun:
+2 252 SpA Life Orb Venusaur Hidden Power Fire vs. 252 HP / 48 SpD Heatproof Cobalion in sun: 307-361 (79.53 - 93.52%) --
guaranteed 2HKO after Stealth Rock
With only a small amount of investment, Cobalion can tank a +2 HP Fire from Venusaur in the sun. Without a boost, it's only a 3HKO at best, and after the weather war is won by your team, it doesn't even come close.
Mind you, Cobalion is still nuked by Volc in the sun with Fire Blast, but not much isn't so I don't find that surprising :P. Also keep in mind that you can run a healthy amount of SpDef investment over Defense in order to use its typing to tank the special hits instead of the physical Fighting-Type attacks that give it trouble.
I think this could use more discussion, so feel free to help me out on this!