Relaxed
252 HP / 48 Defense / 208 Special Defense
Payback
Earthquake
Rapid Spin
Toxic Spikes
Toxic Spikes eliminate many grounded pokemon, like Blissey, Celebi, Swampert and Raikou, all of which are threats to Suicune. Lead Adamant Mamoswine Earthquake 4HKOs unless it rolls max damage all three times while Swampert Earthquake caps at 25%. 56 Special Attack Hydro Pump will almost always 3HKO, but will often miss at least once. Surf always 4HKOs, regardless of the damage roll. I'm experiment with different EV spreads. Might even go back to max HP / max special defense. The added move coverage of Earthquake lets me hit Magnezone so I don't ALWAYS need Shed Shell (Earthquake OHKOs Magnezone after Stealth Rocks about 33% of the time, always with residual damage). Payback hits Celebi and Rotom to help wear them down so Suicune can sweep. I'm running Relaxed so I'm slower then other Forretress, which lets me spin their layers away as they lay them. Many common leads are set up on, and those that aren't are normally open to a quick switch to Tyranitar (Azelf)
Adamant
252 HP / 16 Attack / 240 Special Defense
Stone Edge
Pursuit
Stealth Rock
Rest
EVed to do a minimum of 95% to Roserade, and to survive anything it does in return before falling to Sandstorm. Special Defense will survive all Gengar Focus Blasts except for Specs, but even LO Gengar Focus Blast will not OHKO 67% of the time. Pursuit is great for picking off Scarfers like Latias, Gengar and Rotom but also can 2HKO a fleeing Tentacruel. Rest works well with Lum Berry to stay alive against repeated volleys from Starmie and Latias but also helps break down Will-O-Wisping Rotoms and negate unforturnate freezes that might let Scarf Starmie live to see another day (or worse, Trick my Suicune). Stone Edge sucks, I would like to find another move.. possibly Ice Punch or Thunder Wave.
Bold
252 HP / 252 Defense / 4 Special Defense
Surf
Calm Mind
Rest
Sleep Talk
The late game immortal. Suicune is virtually unstoppable after a Calm Mind. Even defensive Zapdos and Celebi fails to 2HKO after a single Calm Mind, and will ALWAYS 4HKO after two. Modest Starmie and Timid Gengar Thunderbolts 4HKO after just a single boost while Suicune easily destroys both of them with STAB Surfs. Even offensive LO Celebi Leaf Storm will not OHKO, and Suicune can actually Rest right in front of it, sponging subsequent hits (it does have a respectable chance of 3HKOing). Physical hitters like Salamence, Lucario and Scizor are playing a dangerous game since the former will be worn down by Stealth Rocks, Sandstorm and Life Orb while the latter two take heavy damage from +1 Surfs. Gyarados can attempt to Dragon Dance alongside me, but like Salamence it will often die to sand and Stealth Rocks. "Cro" Gyarados almost always loses one on one since it needs to be at +5 before Waterfall 3HKOs, and +6 for a guarenteed 3HKO. Depending on the EV spread, Surf will 3HKO Gyarados on average at +4 with a 252/176 spread, and with a physically inclined set a 3HKO is likely at just +3.
Blah blah blah, if I can avoid Trick and Explosion Suicune is immortal. All calculations assume Sandstorm is active.
Timid
252 HP / 252 Speed / 4 Defense
Calm Mind
Dragon Pulse
Recover
Reflect
HP Fire means opposing Gengar can speed tie with Latias AND fry Forretress with its own HP Fire so I'm running Reflect instead. Reflect deals with Scizor well enough anyway. Blissey isn't 2HKOed by +6 Dragon Pulse but Latias always beats it with Toxic Spikes so the 128 Special Attack EVs don't seem that important to me, as opposed to sponging Reflected Pursuits. Specially Defensive Skarmory is always 2HKOed by +6 Dragon Pulse so next to Blissey, nothing will last against Latias on stall. Reflect is not just for letting Latias survive her counters but also assists Suicune since Gyarados and Salamence die horribly if Suicune has Reflect up.
Jolly
252 HP / 252 Speed / 4 Defense
Taunt
Toxic
Earthquake
Roost
216 Speed wasn't enough, as I often lost the speed tie with other Gliscors. 220 was unreliable too, and I eventually used 236 before giving up and just maxing it. Now the majority of Zapdos, Roserade, Gliscor and Salamence are outrun. Throwing around Taunt catches things like Rotom and Latias from dropping a Trick and random Brelooms from Sporing. Taunt and Roost together eliminate many stall pokemon such as Skarmory and Foretress, who are PP stalled. Speed lets Gliscor take on non-scarfed Heatran somewhat reliably, as Flamethrower doesn't do enough and Fire Blast misses behind my Sand Veil. Counters any Tyranitar without Ice Beam and switches in on most sleep moves with around a 50% chance of them missing outright (52% chance of Hypnosis missing and 40% chance of Sleep Powder crapping out). Toxic takes out Rotom and wards off Blissey while beating defensive Celebi nearly all of the time. Celebi Grass Knot tops at 27% while Roosted HP Ice doesn't even 2HKO.
Jolly
252 Speed / 252 Attack / 4 HP
Iron Head
Thunder Punch
Fire Punch
Trick
The cleanser, hunter and threat checker. Jirachi matches +1 Jolly Salamence and beats virtually every other pokemon in OU. If something starts to set up, more often then not Jirachi can flinch it to hell it or lock it in place with Trick. Iron Head deals sufficient damage that anything hurt by Toxic Spikes is often killed before even firing a single shot. Sandstorm wears down opponents fast enough that Gyarados and Salamence can sometimes be KOed by resisted Iron Heads. Nasty Plot Azelf, Breloom, Lucario, Gengar and random other stuff I couldn't ever dream of facing are obliterated before they can cause much damage. I would like to use U-Turn over Thunder Punch, but I'm too easily beaten by Gyarados.