Which Pokemon have had changes to stats, abilities or their movepool in Pokemon Sun/Moon?

Solution 1:

These are the gains and nerfs that I know of so far:

Beartic
Gained: Slush Rush (Speed Boost in Hail)
Boldore and Roggenrola
Gained: Weak Armor (Lowers Defense, but raises Speed two stages when hit with a Physical attack)
Entei
Changed: Flash Fire -> Inner Focus (Can't be flinched)
Gengar
Changed: Levitate -> Cursed Body (May disable the enemy's move when hit with a move that makes contact)
Gigalith
Gained: Sand Stream (Starts a Sandstorm)
Pelipper
Gained: Drizzle (Starts Raining)
Raikou
Changed: Volt Absorb -> Inner Focus (Can't be flinched)
Suicune
Changed: Water Absorb -> Inner Focus (Can't be flinched)
Torkoal
Gained: Drought (Starts Intense Sunlight)
Vanilluxe
Gained: Snow Warning (Starts a Hailstorm)

Alakazam (Mega)
SpDef +10 (95 -> 105)
Arbok
Atk +10 (85 -> 95)
Ariados
SpDef +10 (60 -> 70)
Beartic
Atk +20 (110 -> 130)
Chimecho
HP +10 (65 -> 75)
Def +10 (70 -> 80)
SpDef +10 (80 -> 90)
Corsola
HP +10 (55 -> 65)
Def +10 (85 -> 95)
SpDef +10 (85 -> 95)
Crustle
Atk +10 (95 -> 105)
Cryogonal
HP +10 (70 -> 80)
Def +20 (30 -> 50)
Delcatty
Spe +20 (70 -> 90)
Dodrio
Spe +10 (100 -> 110)
Dugtrio
Atk +20 (80 -> 100)
Electrode
Spe +10 (140 -> 150)
Exeggutor
SpDef +10 (65 -> 75)
Farfetch’d
Atk +25 (65 -> 90)
Illumise
Def +20 (55 -> 75)
SpDef (75 -> 85)
Lunatone
HP +20 (70 -> 90)
Magcargo
HP +10 (50 -> 60)
Sp. Atk +10 (80 -> 90)
Mantine
HP +20 (65 -> 85)
Masquerain
Sp. Atk +20 (80 -> 100)
Spe +20 (60 -> 80)
Noctowl
Sp. Atk +10 (76 -> 86)
Pelipper
**Sp. Atk +10 (85 -> 95)
Qwilfish
Def +10 (75 -> 85)
Solrock
HP +20 (70 -> 90)
Swellow
Sp. Atk +25 (50 -> 75)
Volbeat
Def +20 (55 -> 75)
SpDef (75 -> 85)
Woobat
HP +10 (55 -> 65)

Bellossom
Gained: Quiver Dance
(Bug - Status - Boosts Sp Atk, Sp Def & Speed by one stage)
Dodrio
Gained: Swords Dance
(Normal - Status - Boosts Atk by two stages)
Gained: Jump Kick
(Fighting - Physical - 100BP/90% Acc - If this misses, the user takes half max HP in damage)
Flygon
Gained: Dragon Dance
(Dragon - Status - Boosts Attack and Speed by 1 stage)
Mantine
Gained: Roost
(Flying - Status - Heals up to 50% Max HP. While perched, the Pokemon is no longer Flying-type
Noctowl
Gained: Moonblast
(Fairy - Special 95BP/100% Acc - May lower target's Special Attack)
Sharpedo
Gained: Psychic Fangs
(Psychic - Physical 85BP/100% Acc - Destroys Enemy Light Screens/Reflects)
Stoutland
Gained: Psychic Fangs
(Psychic - Physical 85BP/100% Acc - Destroys Enemy Light Screens/Reflects)
Wormadam
Gained: Quiver Dance
(Bug - Status - Boosts Sp Atk, Sp Def & Speed by one stage)