Details: Like all Battle Facilities, there are given rules to The Battle Tree. All battling modes have the standard flat rules that prevent two of the same Pokemon Species and Items attached to such. There are also a list of Banned Pokemon that are prevented from being used, mainly Legendary and Mythical Pokemon. Not all Legendary Pokemon, however, are banned, such a the Island Guardians and Ultra Beasts.
Battle Tree Banned Pokemon:
Mew
Lugia
Celebi
Kyogre
Jirachi
Deoxys
Palkia
Phione
Manaphy
Darkrai
Shaymin
Arceus
Victini
Zekrom
Keldeo
Meloetta
Genesect
Yveltal
Diancie
Hoopa
Volcanion
Cosmoem
Lunala
Marshadow