S doesn't really stand for anything, in the same way A, B, C, and D don't really stand for anything. S rank was created in Japanese video games in order to make more achievement.
Source:
http://www.giantbomb.com/s-rank/3015-2962/
On topic, there's one Victini set that was mentioned previously very briefly and went under the radar, but is actually fucking amazing. Before you all jump on the "wtf kitten stop posing stupid shitty gimmicks that don't ever work" train, just take a moment to look at this awesomeness.
Victini @ Weakness Policy
Ability: Victory Star
EVs: 252 HP / 252 Atk / 4 SpD
IVs: 0 Spd
Brave Nature
- V-Create
- Trick Room
- Bolt Strike
- Grass Knot
With minned speed, Victini reaches 184 before any V-Create "boosts". This means that it'll be "outspeeding" base 75s in Trick Room - in other words, if it can set up on anything base 75 or above, it's basically set. Lets look at some attacks coming from pokes above base 75 that will trigger Weakness Policy.
252 Atk Mega Aerodactyl Stone Edge vs. 252 HP / 0 Def Victini: 338-398 (83.6 - 98.5%) -- guaranteed 2HKO
252+ SpA Mega Launcher Mega Blastoise Water Pulse vs. 252 HP / 4 SpD Victini: 332-392 (82.1 - 97%) -- guaranteed 2HKO
+2 4 SpA Suicune Scald vs. 252 HP / 4 SpD Victini: 318-374 (78.7 - 92.5%) -- guaranteed 2HKO
252+ SpA Kingdra Surf vs. 252 HP / 4 SpD Victini: 260-308 (64.3 - 76.2%) -- guaranteed 2HKO
0 Atk Mew Knock Off (97.5 BP) vs. 252 HP / 0 Def Victini: 140-166 (34.6 - 41%) -- guaranteed 3HKO
252 Atk Krookodile Earthquake vs. 252 HP / 0 Def Victini: 306-360 (75.7 - 89.1%) -- guaranteed 2HKO
252+ Atk Metagross Earthquake vs. 252 HP / 0 Def Victini: 248-292 (61.3 - 72.2%) -- guaranteed 2HKO
252 SpA Mega Houndoom Dark Pulse vs. 252 HP / 4 SpD Victini: 276-326 (68.3 - 80.6%) -- guaranteed 2HKO
252+ SpA Hydreigon Dark Pulse vs. 252 HP / 4 SpD Victini: 278-330 (68.8 - 81.6%) -- guaranteed 2HKO
252 Atk Life Orb Mienshao Stone Edge vs. 252 HP / 0 Def Victini: 278-328 (68.8 - 81.1%) -- guaranteed 2HKO
252+ Atk Choice Band Heracross Knock Off (97.5 BP) vs. 252 HP / 0 Def Victini: 340-400 (84.1 - 99%) -- guaranteed 2HKO
252+ SpA Choice Specs Kyurem Earth Power vs. 252 HP / 4 SpD Victini: 322-380 (79.7 - 94%) -- guaranteed 2HKO
252 Atk Life Orb Sharpedo Waterfall vs. 252 HP / 0 Def Victini: 322-382 (79.7 - 94.5%) -- guaranteed 2HKO
252 SpA Shaymin Earth Power vs. 252 HP / 4 SpD Victini: 164-194 (40.5 - 48%) -- guaranteed 3HKO
Unlike most relatively gimmicky WP shit, Victini can tank some fucking hits. These are some of the strongest attacks in the entire tier - some of them STAB, and all of them super effective, and yet Victini can take them, get +2/+2, Trick Room to be faster than the entire team, and proceed to absolutely fucking wreck.
I don't want to mislead you guys, it's not like you can only set up on faster threats. There are plenty of slower but weaker threats that this strategy works on similarly, it's just on a case-by-case basis. It's also worth noting that this Victini loves Sticky Web, as it allows it to set up easily on stuff like Swampert.
This post is partly to inform you guys of a fucking amazing possibility to use with Victini that can wreck face, and to contend that it should be considered in its viability, but it's also to just show how a set that would normally be so gimmicky can work wonders on a diverse poke like Victini. When you have access to very respectable bulk and a diverse support movepool, the possibilities really are endless.