this has been repeated over and over by people I really respect as HO users and as stall players but I still don't see how it is true so can someone explain please
lets say special offense teams consist of 6 of the following
azelf / gengar / infernape / latias / starmie / jolteon / empoleon / heatran / suicune / mismagius
azelf gengar and heatran can explode on blissey
infernape can beat her with focus blasts
[...]
I understand the weaken the walls argument but I just don't understand how it works against blissey unless they try to use it to wall infernape or get blown up or something
Sorry, reading this thread backwards and I thought this was inadequately answered. If half your team kills Blissey (and if you don't have 3 guys who kill her, I'm pretty sure you're doing it wrong), then they really do have to choose between losing all their monsters or bringing in Blissey to be slaughtered. Against Blisseys heavily EV'd in Special Defense (i.e. good ones), the "just keep attacking" plan really doesn't work; I think Blissey is unique among walls in being able to boast this. However, it is easy to run a ton of pokes that both do their job killing things in general, and also make Blissey go away when called upon.
Gengar, as noted in the Greek RMT, almost always lures Bliss, and otherwise really does just dismantle people. Heatran can also come in easily on Fire Blasts, Bullet Punches or other sucky choiced moves and start killing things until Blissey shows up. Heatran also has the benefit of being able to fake people out extremely hard, with something like Sub + LO + Explosion. For some reason, people never seem to expect the Explosion from SubTran. Further, you can scout them with Sub until you feel really confident that you'll explode successfully. Azelf and Infernape also kill Blissey no problem. Even Starmie can run Pain Split now, which is really comparable to Recover in its ability to let you regain HP lost to LO, except it also means Blissey will eventually run out of Softboils if she tries to take you 1v1; Gengar and Mismagius also have this option if desperate. And there's always the hard way, CMing someone up and running Blissey out of healing PP. Basically, it is incredibly unlikely that someone will hide their Blissey, accept uninterrupted beatdown of their pokes, successfully kill the 3-5 members of your team that have some means of ruining Blissey, and then spring her on you for a game win. Even against quite good players, it is not really that difficult to make Blissey die.
I keep hearing that Latias is a problem for special teams, and maybe I just don't run into good ones, but it never seems to be a problem for me. If she's Choiced, you sacrifice a poke and set something up, basically just go about your day. If she's not Choiced, you get to exploit one of the special team's big advantages: your monsters are fast. Azelf, Jolteon, Starmie and Raikou all outspeed her straight-up, and Gengar or your own Latias can coinflip her if you're desperate/she comes in on you. I guess if you let Latias set up Calm Minds unmolested she'll kill you, but I don't think there's a HO team that doesn't get destroyed if it lets the opponent set up relevant sweepers, so it's at least not uniquely vulnerable in this regard.