Ho , Yesterday i've tried to go Battle boss nikola cause i losed the opportunity years ago ti cartch celeby, and nothing....he Say "fighing me now Will not be of use "....release regirock and vulcanion , tried another time and nothing....the same thing....nothing start and nothing spawn.....can resolve this bug ?

Hello @Mirkotidus91. My apologies for the late response.

 

According to our database, you have not completed the Celebi quest on this account. 

Nikola boss does not spawn Volcanion. Instead, Volcanion respawns when you re-enter the area you caught it in.

According to our database, you selected Registeel from the quest. So, you most likely caught it in Birth Island. Nikola does not respawn Legendary Pokémon caught in Birth Island.

I have gone ahead and restored your Regirock, but for Celebi you'll need to finish the quest for it and for Volcanion simply return to where you originally caught it.

 

Let me know if you have further questions.