No, Leon Isn't Fighting Ash With Eternatus In The Master's Eight

thegamer.com:

Some of the promotional shots for this weekend’s episode of Pokemon are causing quite a stir online. The art depicts Ash, Goh, and the current Monarch of the World Coronation series, Leon. Between them is Eternatus, the Legendary Dragon Pokemon who once threatened all of Galar in Sword & Shield. With the Master’s Eight Finals on the horizon, this image would seem to suggest that Leon has been secretly holding Eternatus throughout the tournament, waiting until the final battle to surprise Ash with this god-tier Legendary.

If you’ve been following Journeys since the beginning, you know that isn’t possible. Here’s what’s probably going on in that promo still and what we can expect to actually happen in the final battle.

Eternatus first appeared at the very beginning of the current series, known as Journeys in the States. Much like the games, Chairman Rose of the Macro Cosmos Corporation hatches a plan to capture Eternatus and exploit its power to generate unlimited energy for all of Galar. Rose discovers Leon at a young age and grooms him to become a champion Pokemon trainer that will one day defeat and capture Eternatus for him. That day comes sooner than expected when Eternatus breaks free from its containment in the energy plant beneath Wyndon. Leon challenges the Pokemon but is unsuccessful in catching it. However, with the help of Zacian and Zamazenta, Ash and Goh are able to weaken Eternatus and capture it together. Technically belonging to Goh, Eternatus is sealed away in an underground vault by Professor Magnolia.

It remained there until this week, when Leon revealed to Ash and Goh he had been working with Professor Magnolia to rehabilitate Eternatus. The Pokemon has an understandable mistrust of people, but Leon