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.