Just in case anyone else was thinking about it! Thanks to Phiddlesticks for helping with this. If anyone has any better ideas for Def training, or you can confirm how many Atk EVs Druddigon gives, feel free to post here.
HP
Surf in the dark puddles of Icirrus City - Stunfisk (100%, 2 HP)
Also, Victini (3 HP) can be rebattled infinitely as long as you do not catch it.
Atk
Route 1 - Lillipup (50%, 1 Atk) and Patrat (50%, 1 Atk)
Dragonspiral Tower 2F - Golett (100%, 1 Atk)
Dragonspiral Tower 1F - Golett (50%, 1 Atk), Druddigon (30%, 2 Atk), Mienfoo (20%, 1 Atk)
Outside of Dragonspiral Tower, Double Grass - Tranquill (30%, 2 Atk), Sawsbuck (30%, 2 Atk), Mienfoo (30%, 1 Atk), Druddigon (10%, 2 Atk)
A couple of notes need to be made here.
- During Winter, the Double Grass location changes up. Druddigon is replaced by Beartic (10%, 2 Atk), which is great, but Tranquill is replaced by Vanillish (30%, 2 SpAtk).
Which of these locations is the best is up to you. If you don't mind keeping track exactly how many EVs you got, Dragonspiral 1F or outside Dragonspiral is the place for you. Outside gives the most EVs at in a short time, especially if you can OHKO two enemies at a time. If you'd rather keep it simple, Dragonspiral 2F or Route 1 are where it's at.
Def
Wellspring Cave - Roggengola (50%, 1 Def)
Pinwheel Forest - Venipede (15%, 1 Def) and Sewaddle (35%, 1 Def)
Pinwheel Forest Double Grass - Whirlipede (15%, 2 Def) and Swadloon (35%, 2 Def)
Chargestone Cave - Klink (29%, 1 Def), Ferroseed (20%, 1 Def), Boldore (10%, 1 Atk, 1 Def)
None of these guarantee a Def encounter. Wellspring Cave also has 50% Woobat, Pinwheel has Cottonee/Petilil (35%) and Pidove (15%), Pinwheel Double has Cottonee/Petilil (35%) and Tranquil (15%), and Chargestone Cave has Joltik (36-39%) and Tynamo (2-8%), depending which floor you're on. Note that Boldore gives 1 Atk in addition to 1 Def!
SpAtk
Celestial Tower - Litwick (100%, 1 SpAtk)
You can go to higher floors if you want, those have Elgyem (15%) which also give 1 SpAtk. There's a Nurse on 3F, which is convenient.
SpDef
Surf in Driftveil City - Frillish (100%, 1 SpDef)
Speed
Surf on Route 3 - Basculin (100%, 2 Speed)
You can Surf in a lot of places for 100% Basculin, but this is an example of a place where you don't have to go through tall grass or anything to get to a surfing spot when coming from a close Poké Center.
HP
Surf in the dark puddles of Icirrus City - Stunfisk (100%, 2 HP)
Also, Victini (3 HP) can be rebattled infinitely as long as you do not catch it.
Atk
Route 1 - Lillipup (50%, 1 Atk) and Patrat (50%, 1 Atk)
Dragonspiral Tower 2F - Golett (100%, 1 Atk)
Dragonspiral Tower 1F - Golett (50%, 1 Atk), Druddigon (30%, 2 Atk), Mienfoo (20%, 1 Atk)
Outside of Dragonspiral Tower, Double Grass - Tranquill (30%, 2 Atk), Sawsbuck (30%, 2 Atk), Mienfoo (30%, 1 Atk), Druddigon (10%, 2 Atk)
A couple of notes need to be made here.
- During Winter, the Double Grass location changes up. Druddigon is replaced by Beartic (10%, 2 Atk), which is great, but Tranquill is replaced by Vanillish (30%, 2 SpAtk).
Which of these locations is the best is up to you. If you don't mind keeping track exactly how many EVs you got, Dragonspiral 1F or outside Dragonspiral is the place for you. Outside gives the most EVs at in a short time, especially if you can OHKO two enemies at a time. If you'd rather keep it simple, Dragonspiral 2F or Route 1 are where it's at.
Def
Wellspring Cave - Roggengola (50%, 1 Def)
Pinwheel Forest - Venipede (15%, 1 Def) and Sewaddle (35%, 1 Def)
Pinwheel Forest Double Grass - Whirlipede (15%, 2 Def) and Swadloon (35%, 2 Def)
Chargestone Cave - Klink (29%, 1 Def), Ferroseed (20%, 1 Def), Boldore (10%, 1 Atk, 1 Def)
None of these guarantee a Def encounter. Wellspring Cave also has 50% Woobat, Pinwheel has Cottonee/Petilil (35%) and Pidove (15%), Pinwheel Double has Cottonee/Petilil (35%) and Tranquil (15%), and Chargestone Cave has Joltik (36-39%) and Tynamo (2-8%), depending which floor you're on. Note that Boldore gives 1 Atk in addition to 1 Def!
SpAtk
Celestial Tower - Litwick (100%, 1 SpAtk)
You can go to higher floors if you want, those have Elgyem (15%) which also give 1 SpAtk. There's a Nurse on 3F, which is convenient.
SpDef
Surf in Driftveil City - Frillish (100%, 1 SpDef)
Speed
Surf on Route 3 - Basculin (100%, 2 Speed)
You can Surf in a lot of places for 100% Basculin, but this is an example of a place where you don't have to go through tall grass or anything to get to a surfing spot when coming from a close Poké Center.