Reducing Passive Damage

Reducing the amount of damage that you take from passive damage (e.g. Burn damage, Sandstorm/Hail damage, Poison damage, Life Orb recoil) can be very beneficial. To do this, we need to know the percentage of HP that these reduce per turn.

Sandstorm/Hail: 6.25% or 1/16 of max HP

Burn: 12.5% or ⅛ of max HP

Poison: 12.5% or ⅛ of max HP, increases by 12.5% every turn for a badly poisoned Pokémon

Life Orb: 10% or ⅒ of max HP

With this in mind, if we want to take one less point of damage we reduce a Pokémon’s HP stat to one under a multiple of 16, 8, or 10, depending on the passive damage you’re trying to reduce. For example, Cresselia often uses 220 HP EVs because this reaches the HP stat of 223. 223 is one under a multiple of 16, which means that Cresselia will take one point less of Sandstorm, Burn, and Poison Damage (Burn and Poison damage are also reduced because 12.5% is a multiple of 6.25%). Why does this work? It’s because the game rounds down for most numerical values, truncating all numbers after the decimal point. In other words, 224 divided by 16 is 14, while 223 divided by 16 is 13.9375, rounded down to 13 points of damage. For certain Pokémon like Cresselia and Togekiss that stay on the field for a long time, it’s a good idea to minimize Sandstorm damage because of the large number of Tyranitars they tend to attract.

Only attempt to reduce passive damage if it will not significantly increase your damage percentages taken from attacks.

Distributing HP for Leftovers/Black Sludge

Leftovers and Black Sludge both recover 1/16 of your max HP rounded down at the end of the turn, so to make sure that you get a whole number of HP recovered, it’s beneficial to have an HP stat that is divisible by 16. Only implement this technique if you won’t take significantly more damage and the benchmark is just a few points above your current HP stat (i.e. don’t reduce your HP stat just for the sake of perfect Leftovers recovery).

Distributing HP for Sitrus Berry

Sitrus Berry restores ¼ of your Pokémon’s max HP, so you want your HP stat to be divisible by four. Similar to Leftovers, getting perfect Sitrus Berry recovery is not a very high priority, so only attempt to do so if you won’t take a higher percentage of damage from attacks. If you prefer not to make the HP stat divisible by four, try to make it an even number. This will cause Sitrus Berry to activate after your Pokémon is hit by Super Fang, making it more difficult for it to be picked off by a follow-up attack. If the HP stat is an odd number, Super Fang would leave you sitting just above 50% HP, preventing Sitrus Berry from activating. Also, if you want to see if your Pokémon will be able to survive two consecutive attacks while factoring in the Sitrus Berry, simply multiply the HP stat by 1.25, then round down. Add up the maximum damage rolls of the two attacks, and if it’s less than your HP * 1.25, you’re good to go!

Distributing HP for Substitute

The move Substitute reduces your HP by ¼ of your max HP (rounded down) to produce a plush doll that bravely takes attacks in place of your Pokémon. To get an optimum Substitute HP benchmark, either make the HP stat one over a multiple of four, or simply make the HP stat not divisible by four. This will allow you to substitute four times with one to three HP leftover. If you’re also holding the item Leftovers, it’s best to make your HP stat equal to 1, 2, 3, 6, 7, or 11 points above a multiple of 16. This allows your Pokémon to create four Substitutes, then have recovered enough HP with Leftovers to create another one (assuming your Pokémon took no other damage).

Source: http://nuggetbridge.com/articles/bulking-guide-defensive-ev-spreads/