Greninja @ Life Orb
Ability: Protean
EVs: 12 HP / 252 SAtk / 244 Spd
Timid Nature
- Ice Beam
- Scald
- Hidden Power [Fire]
- Protect
Pretty standard from what I've seen so far. Protect is the "stand-out" idea I had though. Protect through Protean changes it to Normal type, which doesn't sound all that great except the priority puts it +1 so you negate an attack and become Normal for the next attack (if you aren't faster than them). 244 Spd makes it faster than all max 120 base Spd's, any extra EVs are pretty much wasted as scarfers will be faster than you anyway.
Math
Offensive
Greninja vs OU Mixed Wall Hippowdon
252 SpA Life Orb Greninja Ice Beam vs. 252 HP / 252+ SpD Hippowdon: 205-242 (48.8 - 57.61%) -- 47.66% chance to 2HKO
252 SpA Life Orb Greninja Scald vs. 252 HP / 252+ SpD Hippowdon: 172-203 (40.95 - 48.33%) -- guaranteed 3HKO
Greninja vs OU Specially Defensive Skarmory
252 SpA Life Orb Greninja Ice Beam vs. 224 HP / 252+ SpD Skarmory: 153-183 (46.78 - 55.96%) -- 23.83% chance to 2HKO
252 SpA Life Orb Greninja Hidden Power Fire vs. 224 HP / 252+ SpD Skarmory: 229-273 (70.03 - 83.48%) -- guaranteed 2HKO
Greninja vs OU Rapid Spin Forretress
252 SpA Life Orb Greninja Hidden Power Fire vs. 252 HP / 4 SpD Forretress: 764-905 (215.81 - 255.64%) -- guaranteed OHKO
Greninja vs OU Standard Forrothorn
252 SpA Life Orb Greninja Hidden Power Fire vs. 252 HP / 208 SpD Ferrothorn: 380-452 (107.95 - 128.4%) -- guaranteed OHKO
Greninja vs OU Specially Defensive Celebi
252 SpA Life Orb Greninja Ice Beam vs. 252 HP / 236+ SpD Celebi: 252-299 (62.37 - 74%) -- guaranteed 2HKO
252 SpA Life Orb Greninja Hidden Power Fire vs. 252 HP / 236+ SpD Celebi: 187-221 (46.28 - 54.7%) -- 7.81% chance to 2HKO
Greninja vs OU Specially Defensive Jirachi
252 SpA Life Orb Greninja Hidden Power Fire vs. 252 HP / 236+ SpD Jirachi: 187-221 (46.28 - 54.7%) -- 7.81% chance to 2HKO
Greninja vs OU Calm Mind Latias
252 SpA Life Orb Greninja Ice Beam vs. 252 HP / 0 SpD Latias: 276-328 (75.82 - 90.1%) -- guaranteed 2HKO
Greninja vs OU Offensive Quiver Dance Volcorona
252 SpA Life Orb Greninja Scald vs. 0 HP / 4 SpD Volcarona: 276-328 (88.74 - 105.46%) -- 31.25% chance to OHKO
Greninja vs OU Bulky Quiver Dance
252 SpA Life Orb Greninja Scald vs. 240 HP / 0 SpD Volcarona: 281-330 (75.74 - 88.94%) -- guaranteed 2HKO
Greninja vs OU Choice Band Tyranitar
252 SpA Life Orb Greninja Scald vs. 180 HP / 0 SpD Tyranitar in sand: 195-229 (50.51 - 59.32%) -- guaranteed 2HKO (w/Sand)
Greninja vs OU Tank Dragonite
252 SpA Life Orb Greninja Ice Beam vs. 252 HP / 4 SpD Multiscale Dragonite: 343-406 (88.86 - 105.18%) -- 25% chance to OHKO (w/Multiscale)
Greninja vs OU Bulky Swords Dance Scizor
252 SpA Life Orb Greninja Hidden Power Fire vs. 252 HP / 216 SpD Scizor: 484-567 (140.69 - 164.82%) -- guaranteed OHKO
Greninja vs Goodra
252 SpA Life Orb Greninja Ice Beam vs. 252 HP / 252 SpD Goodra: 218-257 (59.89 - 70.6%) -- guaranteed 2HKO
Greninja vs Sylveon
252 SpA Life Orb (custom) Ice Beam vs. 252 HP / 252 SpD (custom): 226-268 (57.36 - 68.02%) -- guaranteed 2HKO
Defensive
Jolteon vs Greninja
252+ SpA Choice Specs Jolteon Volt Switch vs. 12 HP / 0 SpD Greninja: 222-262 (77.08 - 90.97%) -- guaranteed 2HKO
252+ SpA Choice Specs Jolteon Thunderbolt vs. 12 HP / 0 SpD Greninja: 301-355 (104.51 - 123.26%) -- guaranteed OHKO
252+ SpA Choice Specs Jolteon Signal Beam vs. 12 HP / 0 SpD Greninja: 158-187 (54.86 - 64.93%) -- guaranteed 2HKO
252+ SpA Choice Specs Jolteon Hidden Power Ice vs. 12 HP / 0 SpD Greninja: 148-175 (51.38 - 60.76%) -- guaranteed 2HKO
252+ SpA Life Orb Jolteon Volt Switch vs. 12 HP / 0 SpD Greninja: 192-227 (66.66 - 78.81%) -- guaranteed 2HKO
252+ SpA Life Orb Jolteon Thunderbolt vs. 12 HP / 0 SpD Greninja: 261-308 (90.62 - 106.94%) -- 43.75% chance to OHKO
252+ SpA Life Orb Jolteon Signal Beam vs. 12 HP / 0 SpD Greninja: 138-162 (47.91 - 56.25%) -- 85.16% chance to 2HKO
252+ SpA Life Orb Jolteon Hidden Power Ice vs. 12 HP / 0 SpD Greninja: 129-152 (44.79 - 52.77%) -- 23.44% chance to 2HKO
Weavile vs Greninja
252+ Atk Life Orb Weavile Ice Shard vs. 12 HP / 0 Def Greninja: 122-146 (42.36 - 50.69%) -- 2.34% chance to 2HKO
252+ Atk Life Orb Weavile Pursuit vs. 12 HP / 0 Def Greninja: 122-146 (42.36 - 50.69%) -- 2.34% chance to 2HKO
252+ Atk Life Orb Weavile Night Slash vs. 12 HP / 0 Def Greninja: 214-253 (74.3 - 87.84%) -- guaranteed 2HKO
252+ Atk Choice Band Weavile Ice Shard vs. 12 HP / 0 Def Greninja: 142-168 (49.3 - 58.33%) -- 98.05% chance to 2HKO
252+ Atk Choice Band Weavile Pursuit vs. 12 HP / 0 Def Greninja: 142-168 (49.3 - 58.33%) -- 98.05% chance to 2HKO
252+ Atk Choice Band Weavile Night Slash vs. 12 HP / 0 Def Greninja: 247-292 (85.76 - 101.38%) -- 12.5% chance to OHKO
Talonflame vs Normal/Water/Ice Greninja
252+ Atk Life Orb Talonflame Acrobatics (55 BP) vs. 12 HP / 0 Def Greninja: 130-153 (45.13 - 53.12%) -- 31.64% chance to 2HKO
252+ Atk Life Orb Talonflame Flare Blitz vs. 12 HP / 0 Def Greninja: 281-331 (97.56 - 114.93%) -- 81.25% chance to OHKO
252+ Atk Life Orb Talonflame Brave Bird vs. 12 HP / 0 Def Greninja: 281-331 (97.56 - 114.93%) -- 81.25% chance to OHKO
252+ Atk Flying Gem Talonflame Acrobatics (110 BP) vs. 12 HP / 0 Def Greninja: 297-349 (103.12 - 121.18%) -- guaranteed OHKO
252+ Atk Flying Gem Talonflame Flare Blitz vs. 12 HP / 0 Def Greninja: 216-255 (75 - 88.54%) -- guaranteed 2HKO
252+ Atk Flying Gem Talonflame Brave Bird vs. 12 HP / 0 Def Greninja: 322-381 (111.8 - 132.29%) -- guaranteed OHKO
Threats
Scarfers
This is pretty obvious. His defensive abilities aren't that great and any scarfers above 65 base Spd(w/positive nature) will be faster, makes pretty much every scarfer a threat.
Chancey, Blissey, Jellicent, Rotom-W, Tentacruel
These walls completely and 100% stop Greninja in it's tracks. It can't even reliably 4HKO+ any of these pokemon.
Talonflame
Talonflame can theaten Greninja due to his amazing ability Gale Wing, which gives him +1 Priority on all Flying moves. This allows Acrobatics / Brave Bird to have priority over Greninja's attacks and easily results in it dying.