From Bulbapedia, the community-driven Pokémon encyclopedia.
Manalo Stadium (Japanese: マナーロ・スタジアム Manalo Stadium) is an anime-exclusive very large floating structure in the Alola region found near Aether Paradise.
It was built by the Aether Foundation to host Alola's first League Conference. It first appeared in The Dealer of Destruction! while it was still in construction, when Professor Kukui announced the Alola League. The construction was completed in Chasing Memories, Creating Dreams!.
It reappeared in League Offenders and Defenders! as some of the entrants for the Manalo Conference signed up and explored some of the stadiums sights. The tournament itself began in the next episode and concluded in Enter the Champion!. The award ceremony was unexpectedly interrupted by the appearance of a Guzzlord. Two more Guzzlord appeared from other wormholes in the next episode, but all three Junkivore Pokémon were successfully sent back to Ultra Space by the end of the episode.
Following the Guzzlord incident, the stadium also hosted an exhibition match between Professor Kukui and the Manalo Conference winner. The match started in Exhibition Unmasked! and ended in From Z to Shining Z!, bringing the Manalo Conference to an end along with it.
Besides the battlefield, the stadium also houses a Pokémon Center, a shopping mall, and multiple restaurants and food trucks.
Manalo Stadium under construction
Manalo Stadium's battlefield
Manalo Stadium's Pokémon Center