Pokémon Ultra Sun and Ultra Moon/Version Differences

There are a lot of differences in Pokemon between Pokemon Ultra Sun and Ultra Moon.

Minor Differences

 * On Illima's Trial, you'll have to fight Totem in Sun and Totem Alolan  in Moon.
 * Sun and Moon are set 12 hours apart, so Sun follows the system clock, whereas Moon's in-game time is transposed 12 hours from the system clock. For instance, if it is 10AM on the system time, the in-game time in Sun will be 10AM, but in Moon it is 10PM.

Solgaleo
is the legendary Pokemon exclusive to Sun version, featured on the box art. Known as the Sunne Pokémon, it's a Psychic/Steel type, making it vulnerable to only 8 types: Fighting, Bug, Water, and Electric (1x), Ground, Ghost, Fire, and Dark (2x). Solgaleo is immune to poison and is resistant to: Normal, Flying, Rock, Steel, Grass, Psychic, Ice, Dragon, and Fairy (1/2x). After summoning Solgaleo, it'll be merged with Necrozma, and you'll be forced to battle it and faint it. Before heading up to battle the Elite Four, if you go to Mahalo Trail, you'll be able battle and catch Solgaleo. When caught, Solgaleo will be level 60. It'll know the moves Cosmic Power, Crunch, Zen Headbutt, and Sunsteel Strike, its signature move. Sunsteel Strike lets it turn into a phase known as Radiant Sun to perform the attack. Radiant Sun changes its color scheme to white and gold, and it glows. It jumps up, summons a giant fire beam that resembles the sun, and charges through the ray to attack its opponent.

Finding Solgaleo is only in the Ultra Sun version, so if you're an Ultra Moon player you must trade in order to receive it.

Passimian
is an Alolan Pokemon exclusive to Sun version.

Turtonator
is an Alolan Pokemon exclusive to Sun version.

Alolan Vulpix
is a Kanto Pokemon that has an Alolan Form. It evolves into Alolan Ninetails and is exclusive to Sun version.

Alolan Ninetails
is a Kanto Pokemon that has an Alolan form. It evolves from Alolan Vulpix and is exclusive to Sun Version.

Buzzwole
(also known as UB-02 Absorption) is an Ultra Beast exclusive to Sun version.

Kartana
(also known as UB-04 Blade) is an Ultra Beast exclusive to Sun version.

Cranidos
is a fossil Pokemon exclusive to Sun version. It evolves into Rampardos.

Rampardos
is a fossil Pokemon exclusive to Sun version. It evolves from Cranidos.

Tirtouga
is a fossil Pokemon exclusive to Sun version. In evolves into Carracosta.

Carracosta
is a fossil Pokemon exclusive to Sun version. It evolves from Tirtouga.

Cottonee
is a Pokemon exclusive to Sun version. It evolves into Whimsicott.

Whimsicott
is a Pokemon exclusive to Sun version. It evolves from Cottonee.

Rufflet
is a Pokemon exclusive to Sun version. It evolves into Braviary.

Braviary
is a Pokemon exclusive to Sun version. It evolves from Rufflet.

Groudon
is a Pokemon exclusive to Sun version.

'Rockruff can only evolve into Lycanroc Midday Form in Sun, and Lycanroc Midnight Form in Moon. However, both evolutions are catchable in the wild.'