Ok, something really odd is that yesterday when I was playing, every team I faced was getting wrecked by SubSeed Breloom. Because of all the ScarfTar around (which seems to be appearing more than Latias and Manaphy IMO :/), teams seem to be skeptical about using Rotom, especially non-scarf ones. I don't think I've seen a single SubRotom, and not very many Celebi either. SubSeed Breloom with a bulky spread easily takes advantage of this provided you don't Spore until you need to.
I decided to give my OU team 'Triple Hit' a try in this ladder, and it works extremely well if I can get enough entry hazards up. It seems that a lot of Latias and Manaphy's checks are grounded pokemon, and they'll lose that 'check' status pretty quickly if they're taking Stealth Rock + Spikes + an attack. While Manaphy obviously isn't on that team since it's an OU team, I can easily take advantage of what everyone seems to be using due to the overpreparation for Manaphy and Latias.
Also, about Wacan Manaphy, I've faced it a couple of times, and honestly, it's too weak without the Life Orb boost, even after a Tail Glow and max Special Attack (with Timid). It couldn't even OHKO my ScarfRotom-C after a Tail Glow, and Rotom-C only had 40 HP EVs, meaning that I just Thunderbolted him as he Surfed, and then Thunderbolted again, breaking through the Wacan, and still surviving with about 3%. Granted, Stealth Rock wasn't up, but Rotom-A isn't very sturdy with only 40 HP EVs.
I'm honestly wondering what's so good about Wacan Manaphy, because after running some calcs, I've come to the conclusion that it doesn't do good against Offense or Stall. Offensive teams generally have a lot of resistances to come in on, and always have at least 1 pokemon with more than 328 Speed (usually more). This means that Manaphy is going to find it hard to get more than one kill against an offensive team, because without any investment in its defenses, it's still going to take a lot more strong neutral attack, easily being revenge-killed, or if something comes in on a Tail Glow or doesn't get OHKOed by Surf, directly killed. Stall teams, on the other hand, carry lots of phazers, entry hazards, Blissey (who completely walls this set unlike the other sets), bulky Waters, etc. In the case of HailStall, there's Abomasnow which wrecks Manaphy. Wacan Manaphy doesn't even have a chance against Stall teams unless all the phazers are gone, Blissey is gone, and it hasn't taken much damage from entry hazards...yeah if that happens, it basically means the Stall team has epically failed and deserves to lose.
It just doesn't seem that Manaphy has the sheer force or double STAB that enabled Garchomp to be so deadly even without Life Orb. Plus, a lot of things do get Energy Ball, Seed Bomb, and Leaf Storm, so it's not as if Manaphy is completely safe.