Gunk Shot Calcs vs Fairies 
44 Atk Life Orb Greninja Gunk Shot vs. 252 HP / 252+ Def Clefable: 296-351 (75.1 - 89%) -- guaranteed 2HKO after Leftovers recovery 
252 Atk Life Orb Greninja Gunk Shot vs. 252 HP / 252+ Def Clefable: 361-429 (91.6 - 108.8%) -- 50% chance to OHKO 
44 Atk Life Orb Greninja Gunk Shot vs. 252 HP / 0 Def Azumarill: 406-478 (100.4 - 118.3%) -- guaranteed OHKO 
44 Atk Life Orb Greninja Gunk Shot vs. 248 HP / 0 Def Togekiss: 351-416 (94.1 - 111.5%) -- 68.8% chance to OHKO 
44 Atk Life Orb Greninja Gunk Shot vs. 252 HP / 220+ Def Sylveon: 330-390 (83.7 - 98.9%) -- guaranteed 2HKO after Leftovers recovery 
252 Atk Life Orb Greninja Gunk Shot vs. 252 HP / 220+ Def Sylveon: 398-471 (101 - 119.5%) -- guaranteed OHKO 
Gardevoir doesn't even need a Calc - It'd dead and gone probably twice over. 
Viable Moves for Greninja 
Water - Hydro Pump, Scald, Waterfall, Water Shuriken (Priority) 
Dark - Dark Pulse, Night Slash 
Ice - Ice Beam, Ice Punch, Blizzard 
Grass - Grass Knot 
Psychic - Extrasensory 
Bug - U-Turn (also provides Pivot) 
Ghost - Shadow Sneak (Priority) 
Fighting - Low Kick, Power-Up Punch 
Rock - Rock Slide 
Flying - Aerial Ace, Acrobatics (Loses Life Orb to use to full potential) 
Ground - Spikes (Entry Hazard) 
Hidden Powers (Fire, Electric, or anything else) 
Very unpredictable.