This mod replaces the battle sprites with sprites from X/Y & OR/AS.
At the end of this post you'll find 4 mods, because PokéMMO doenst support large mods yet.
facus26 fixed the gifs so you can use this mod without buggy gifs! thanks to you, facus ;)
Instructions:
go to mega, open the folder BattleSprites ORAS XY > latest download .zip file(s) place it in your pokemmo/data/mods folder start the game click Mod Management set desired mod(s) to active Save and restart