A Guide to EV Training with Hordes

I want to ask, do power items double power items? a 2 EV mob will turn into 2(2+4) = 12. Or is it 2(2) + 4 = 8? Just wanted to get a clarification for when I EV train pokemon with things like 88 attack.
Power items always give +4 to whatever stat they are per Pokémon. So if you had a Power Anklet and you defeated 5 Zubats; each Zubat gives +1 Speed EV, which is then boosted to +5 because of the Anklet. The total EV yield would be +25 Speed EVs (which could be doubled by having Pokérus).
 
A question on using the Power items? Does the Pokemon I am using to battle the hordes need to hold the Power item, or the Pokemon I'm training via Exp. Share?
The Exp. share distributes all EVs to every Pokémon in the party regardless of what items they hold, so give the Power item to the 'mon you're battling with. All of the EVs it earns will also be earned by the other party members.
 
The Exp. share distributes all EVs to every Pokémon in the party regardless of what items they hold, so give the Power item to the 'mon you're battling with. All of the EVs it earns will also be earned by the other party members.
Wrong. The power item only increases EVs on the mon holding it. All other mons with Exp Share will gain whatever amount of EVs the defeated mons give.

Take, for example, a horde of Wingull. Each gives 1 Speed EV, for a total of 5 Speed EVs if you defeat them all. Now, you have, say. a Greninja battling, with a Talonflame in your party. The EXP Share is on. Greninja is holding the Power Anklet (+4 Speed EVs). After Greninja Surfs to kill all the Wingull, your Greninja will now gain 1 + 4 = 5 EVs times 5 for a total of 25 Speed EVs. Your Talonflame, however, since it was not holding any Power item, will gain only 5 Speed EVs.
 
Wrong. The power item only increases EVs on the mon holding it. All other mons with Exp Share will gain whatever amount of EVs the defeated mons give.

Take, for example, a horde of Wingull. Each gives 1 Speed EV, for a total of 5 Speed EVs if you defeat them all. Now, you have, say. a Greninja battling, with a Talonflame in your party. The EXP Share is on. Greninja is holding the Power Anklet (+4 Speed EVs). After Greninja Surfs to kill all the Wingull, your Greninja will now gain 1 + 4 = 5 EVs times 5 for a total of 25 Speed EVs. Your Talonflame, however, since it was not holding any Power item, will gain only 5 Speed EVs.
I apologize for the misinformation; I was under the impression the mechanics worked the way I discussed. Thank you for the correction ^_^
 
Hey, I just wanna put it out there that Tropius can learn Sweet Scent AND Fly AND gets two nice spread options in Razor Leaf and Earthquake. Slap a wide lens on him and you won't even miss with Razor Leaf.
 
Held items only affect the Pokémon holding them.
Okay, well I just got done fainting off a horde of Trevenant, which give off 2 EV's each in attack. I'm EV training my Froakie right now, who started off with 7 EV's and has Pokerus. How many EV's did he gain off of me killing the horde? I'm assuming he got 20 since he's not holding a power item.
 
You should mention that the best spots for getting Attack EVs can have rain in the overworld, which would prevent you from using Honey or Sweet Scent. In that case, the best EV training sport would probably be the forest for Trevenant (2 Atk, uncommon sadly).
 
I have a question. I was ev training my power bracer equipped pokerus hopip and ko'ed a horde of weepinbell, I should have got 100 evs right? I actually only got 60. What happened?
 
So if the Pokemon that is battling is holding the power item, does that give all the other pokes in the team the same bonus? or do I have to switch around the power item as the EVs go up?