From Thursday, December 1st, 2022 at 4:00 p.m. PST to Sunday, December 4th, 2022 at 3:59 p.m. PST, players of Pokémon Scarlet and Pokémon Violet can battle Charizard who will appear in 7-star Tera Raid Battles at black crystals.

Prepare Yourself for Tera Raid Battle Events and a Special Pokémon Distribution!

Look forward to encountering Charizard and Eevee in Tera Raid Battles, and receive a special Pikachu that knows Fly!

As you embark on your newest Pokémon journey through Paldea, take a moment to receive a special Pokémon via Mystery Gift. You can also expect Tera Raid Battle events to hit the region soon. Learn more about the events coming to Pokémon Scarlet and Pokémon Violet in the coming weeks.

An “Unrivaled” Charizard Blasts into Tera Raid Battles

Catch a Charizard with the Mightiest Mark! This Charizard will appear in 7-star Tera Raid Battles at black crystals from Thursday, December 1, at 4:00 p.m. PST to Sunday, December 4, at 3:59 p.m. PST. This Charizard will then reappear in black crystal Tera Raid Battles on Thursday, December 15, at 4:00 p.m. PST and will make its exit on Sunday, December 18, at 3:59 p.m. PST. Charizard cannot normally be encountered in Paldea, and the Charizard appearing during this event has Dragon as its Tera Type, making it a formidable foe. Work together with friends to topple this powerful Tera Pokémon.

Source: https://www.pokemon.com/us/pokemon-news/prepare-yourself-for-tera-raid-battle-events-and-a-special-pokemon-distribution