Hello, I'm one of the translators for USUM, couple things to look out for:

Pokemon Hair Styling is back, you can change Furfrou, A-Dugtrio, A-Jynx.

Furfrou has the same options as XY, as well as one based on Lunaaa, and the other on Solgaleo.
A-Dugtrio has 4 cuts, each represent a style of music (Normal - Metal, Mohawk - Punk, Dreads - Reggae, Pompadour - Elvis/Rock&Roll)
A-Jynx gets four based on NPCs - Cynthia, Misty, Maylene, Elesa (BW=US, BW2=UM).

23 new A-formes, 6 from kanto, 6 from Johto, 5 from Hoenn, 6 from Sinnoh.

Butterfree - Psychic/Bug
Doduo - Flying/Fighting
Dodrio - Flying/Fighting
Psydick - Ice
Golduck - Ice/Psychic
Jynx - Fairy/Ice

Sentret - Ground
Furret - Ground/Fire
Bellossom - Grass/Fairy
Murkrow - Psychic/Dark
Girafarig - Fire/Ice
Sneasel - Steel/Dark

Trapinch - Bug
Vibrava - Bug
Flygon - Bug/Dragon
Zangoose - Poison
Seviper - Ground

Luxio - Dark/Electric
Luxray - Dark/Electric
Gastrodon - Water/Poison
Rotom - Electric/Steel (Dex)
Weavile - Steel/Dark
Honchkrow - Psychic/Dark