All EVs a Pokemon has must be divisibly by 4, as a stat increases by 1 every 4 EVs.
Scizor's EVs should be 248 HP/252 Atk/8 SDef.
Mandibuzz's EVs should be 248 HP/136 Def/108 SDef/16 Spe to outspeed max Speed Mawile and Azumarill.
The raw power of Hydro Pump is preferred over the burn chance of Scald, as Greninja isn't exactly the strongest Pokemon out there. Put Extrasensory somewhere on it, since dealing with Mega Venusaur and Keldeo is important, preferably over Dark Pulse or Hidden Power.
Metagross has fallen out of favor because of the nerfs it received (weaknesses to Dark/Ghost, Meteor Mash weakened). While Aegislash also suffers from the same weaknesses, it has more power than Metagross when it attacks. Another Assault Vest user is Conkeldurr, who benefits greatly from the item, as its weak Special Defense gets patched up:
Aegislash:
-Shadow Ball
-Shadow Sneak/Sacred Sword
-Iron Head/Sacred Sword/Pursuit
-King's Shield
Nature: Quiet
EVs: 244 HP/12 Def/252 SAtk
Item: Leftovers/Spooky Plate/Spell Tag/Air Balloon
or
-Substitute
-Toxic
-Shadow Ball
-King's Shield
Nature: Modest
EVs: 244 HP/12 Def/252 SAtk
Item: Leftovers
or
-Shadow Ball
-Shadow Sneak
-Flash Cannon/Sacred Sword
-Pursuit/Sacred Sword
Nature: Hasty/Naive
EVs: 4 Atk/252 SAtk/252 Spe
Item: Life Orb
or
-Swords Dance
-Shadow Sneak
-Shadow Claw/Iron Head
-Sacred Sword/Head Smash
Nature: Adamant
EVs: 252 Atk/4 SDef/252 Spe
Item: Life Orb
Conkeldurr:
-Drain Punch
-Mach Punch
-Knock Off
-Ice Punch/Stone Edge
Nature: Adamant
EVs: 252 Atk/236 SDef/20 Spe
Item: Assault Vest
Ability: Guts
Charizard Y should move the last 4 EVs to either defense, since putting them in HP makes the stat even, making Charizard die to 2 Stealth Rock switch-ins instead of 3.
Thx. I may use Conkledurr cause with Scizor I have enough steel-types. And Guts instead of Iron Fist?
One other little thing: Garchomp's nature should be Jolly instead of Adamant, so it gets the most out of its base 102 Speed. That Speed is one of the reasons why Garchomp is probably the most popular Dragon out there. Jolly lets it outspeed other Choice Scarf users.
Thx 2u too. I was thinking to put Ditto Choice Scarf instead of Garchomp. What do you think?