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
Ho-Oh
Celebi
Groudon
Jirachi
Deoxys
Dialga
Phione
Manaphy
Darkrai
Shaymin
Arceus
Victini
Reshiram
Keldeo
Meloetta
Genesect
Xerneas
Diancie
Hoopa
Volcanion
Cosmoem
Solgaleo
Marshadow