The Special Battle rules for Season 8 have been revealed. Season 8 will run from January 13th 2015 to March 16th 2015 and runs on both X & Y and Omega Ruby & Alpha Sapphire, each following the standard league rules each game sets (Gen VI native only in ORAS and allowed to use transferred Pokémon in XY). The base rules for this season are as follows:
Battle type: Double Battle
Pokémon Restrictions: National Pokédex except Mewtwo, Mew, Lugia, Ho-Oh, Celebi, Kyogre, Groudon, Rayquaza, Jirachi, Deoxys, Dialga, Palkia, Giratina, Phione, Manaphy, Darkrai, Shaymin, Arceus, Victini, Reshiram, Zekrom, Kyurem, Keldeo, Meloetta, Genesect, Xerneas, Yveltal, Zygarde, and Diancie
Item Restrictions: Only Berries can be used. Any other items, including Mega Stones, cannot be put on your Pokémon
The other standard rules apply, including reduced to Level 50 if above that, and you choose 4 Pokémon out of your 6.