This thread is full of a lot more "stupid" then I expected. Maybe just resurrect the old Manaphy discussion posts where there was at least some thoughtful discussion. There are like the same 4 people posting over and over that it's broken because of wah wah wah.
So with a couple of Tail Glows, a Life Orb'd Manaphy could potentially 2hko Blissey. That would most likely require the Manaphy to run Surf/Tail Glow/Rain Dance..unless you want to constantly have to lose your Tail Glow for rain support(which sucks b/c there are no OU weather inducers). Then, that set could potentially 2hko Blissey after a couple of Tail Glows. (btw it took 2 Tail Glows to do 51% to the Blissey on the Pokemonexperte.de server) I guess that'd be doing a disservice to the metagame, because people would have to STOP RELYING ON A SINGLE SPECIAL WALL to wall all your special sweepers.
Manaphy suffers greatly from 4 slot syndrome. I'd suggest the best way to use it without having rely on anything from any other poke would be: Rain Dance/ Surf /TG/ Rest. That way, Abomasnow, or Hippodown, or anyone else who can stir up the weather on a switch wouldn't be able to stop you dead in your tracks, you'd have to start up Rain again, but oh well it's only one turn in which you can be roared, wood hammered, whatever else. Then, once you have that down, nothing like Vaporeon, Suicine, Blastoise (105sdef), Kingdra (25% from water), Mantine, Tentacruel, Poliwrath(y hello thar setup bait), Politoed, Slowking, Milotic, Toxicroak, Parasect(loljk), Ludicolo, could come in and stop you because you can't do a thing to them. Except for stat up and hope for a crit.
So we say "oh snap!" we need Ice Beam, or Grass Knot, or HP Electric or else we are pretty much walled to hell and back by these pokes. Ok so we have to drop Rain Dance, Rest, or Tail Glow. Oops, there goes the all self reliant Manaphy.
Dropping Rain Dance means any other auto-weather inducer, or even a poke with TM 11, TM 07, or TM 37 can switch in and make Manaphy have to switch out to get that 1.5 boost/hydration benefit back.
Dropping Rest is probably the best option, but then it can be brought down quick enough by a Specs thunderbolt, or two thunderbolts from most other special sweepers. It's not like there is more than 1 electric types that have over 100 speed though.
So we say, eff it lets drop Rain Dance! Well there goes that rain you depend on for your two favorite benefits, Hydration and 1.5% boost on your surf because there are several OU auto-weather inducers.
Ok, so no Tail Glow! Well that's pretty silly. Good luck though. The ever present CM-Suicine still doesn't have a problem with HP Electric, and has roar. I run haze on my Vappy anways, so he's got no problems: Just a stall war that Vaporeon would win.
If Manaphy had 8 move slots, then it would potentially be an end all poke, but it doesn't.
It sure would be a mindfuck though, to not see Heatran every single match. And people might have to use something else for a special wall(shit!). Just because Blissey can't stop a special sweeper means it's broken? Blissey can't stop a HP Fighting Mismagius after a few CM's either.
I look forward to the testing.
Also: Kingdra usage would effing skyrocket (cool ass beans!)