as a lead, scares Cloysters out, encores Jolteon's subs, and often can get something such as Snorlax Toxiced on the switch. later on in the game, is probably the best perish trap counter, and can potentially stall out Zapdos, Electabuzz, Gengar, and random shit like Dynamicpunch Dragonite, who the rest of the team can have some trouble with.
probably the best spinner in the game, and when you have a toxistall oriented team, you have to get those spikes out as efficiently as possible, and Gengar isnt doing anything to stop me spinning them away carrying Psychic, which also happens to counter Machamp and Tentacruel, both of which can tear through the rest of the team easily enough. Misdreavus is usually a wasted slot anyway with Raichu waiting to come in.
all stall teams need to be able to stop Snorlax, and while Skarm has trouble against the Fire Blasting sets, Tyranitar shuts them down cold. Roar is absolutely awesome here because it works off the toxic/spikes support while 100% countering Skarm's attempts to blow it away. Earthquake would be nice to have, but I can't afford to have it's health worn away by Spikes or Toxic especially without a beller, and once it gets started its really not getting stopped anyway by too much.
Toxic is there to hit fellow Cloysters and Starmies to give me an upper hand in the stallfest, Rest is once again there so I don't get killed by Toxic or Spikes with the lack of a beller, and Surf is a much stronger choice than Ice Beam due to its ability to hit Forretress and Cloyster for some decent damage.
spread more Toxic love, how can you not love this guy? the one common Pokemon that can sort of counter it without taking a Toxic is Gengar, and even Gengar is rarely going to be carrying Rest, so good luck trying to stop repeated Flamethrowers while taking Spikes damage. doesnt immediately kill, but works with the rest of the team to create little chinks in the armor of a standard stall team to eventually reach the point where it can't handle the combined assault of Lax and Tar.
stops cursers cold. besides for further countering Curse, Sand-Attack also cripples basically everything that is going to be switching in, forcing another switch into the spikes AND has a lot of PP if it ever gets to that point.