Speed - Very Important Stuff
Speed is weird in this metagame, considering the fact that everything has the same base speed of 100. You would think that this means that all spreads should either have 252+ Speed or no/4 speed (outside of speed creep), but this isn't always true. This mainly applies to Pokemon that can boost their speed, including Pokemon that set-up (Dragon Dancers are an example of this), Pokemon that have abilities that boost their speed (Speed Boosters and Unburden), or simply Pokemon with a Choice Scarf move. So here's some odd Speed EVs that you can use. A general rule I think is that
44 Speed EVs is all you really need if you have a way to boost your speed outside of Choice Scarf. At 44 Speed EVs, you outspeed anything that doesn't run speed and speed creepers (unless they're doing some extreme speed creeping). At +1 you outpace everything that run max speed, and at +2 you outpace everything at +1, which includes Choice Scarfers. This also means that you can run a bulky choice scarf set with 44 Speed EVs if you so desire. 44 Speed also lets you run a Modest or Adamant nature, making your pokemon stronger than the others in comparison. So the main speed tiers you need to keep in minds are (in order of fastest to slowest). Note that this doesn't include speed creeping. (I'll calc -1 speeds later)
- +1 252+ EVs (Choice Scarfer)
Speed Creeping - Why it's so important
Speed Creeping is the act of tossing a few Speed EVs on a Pokemon that would normally run at most 4 speed EVs. This is prominant in bulky attackers and walls that wish to be faster. Speed Creeping is a way to avoid Speed Ties most of the time, and it is rather useful. However, make sure you don't invest too much into your speed - you still want that bulk. 8-12 speed EVs seems like it is the best to use. Note that max speed pokemon cannot be sped crept or speed creep, as they hit their maximum speed.
Being Slower
While speed is
very important, sometimes you want to be slower. An important example of this is Analytic Pokemon. These Pokemon want to go last so they can get their x1.3 boost. Fortunately, it's pretty easy to be slower than everything because everyone has the same speed. Simple set your Speed to 0 EVs / 0 IVs and a - Speed nature and you should be slower than everything bar other pokemon that are doing the same. Another example of pokemon that would want this is Volt-Switchers and U-Turners so they can get momentum. Sleepers might also want to be slower so that they can get as many sleep turns as possible.
Speed Drops
It is important to note that, if you are at -1 speed, and your opponent is at neutral speed, unless you are scarfed, or your opponent is running a -speed nature and 0 Speed IVs, they will
always outspeed you. A base 100 Pokemon with 252 EVs and a positive nature reaches 328 speed, which becomes 218 at -1 (328x2/3 = 218.666667, which rounds down to 218). A base 100 Pokemon with a neutral nature and 0 EVs hits 236 speed. -1 Speed effectively cancels out Choice Scarf, so if you are scarfed at -1 speed, whoever has more speed investment will move first.