Well, it’s been awhile since there has been a 7-star Tera Raid Event in Pokémon Scarlet & Violet, but from now until July 9, 2023 at 4:59pm PDT / 7:59pm EDT (23:59 UTC) you’ll be able to fight against a Fairy Tera Type Delphox in 7-star Tera Raids. This Delphox has the Mightiest Mark, granting it the title “Delphox the Unrivaled” when sent out in battle.
Before you can challenge Delphox, you’ll first need to have unlocked 6-star Raids, which is something you can do after beating the game and doing some of the postgame stuff. The Delphox raids will then appear in the Black Tera Raid Crystals on the map similar to the other 6-star Raid Crystals, though you’ll be able to tell it’s Delphox due to it being Fairy Tera Type. Even if you don’t have it unlocked yet, you can still join other players if they have unlocked it and you have the Link Code or are playing with friends.
According to Serebii.net’s coverage, it knows the moves Fire Blast, Psychic, Dazzling Gleam, and Will-O-Wisp. It also has the additional moves Magic Room and Nasty Plot, and Dazzling Gleam a second time, meaning it will use Dazzling Gleam at certain intervals against all players. It also has the Ability Magician, which is its Hidden Ability.
If you’re looking for a guide for where to EV train your Pokémon to challenge Delphox, you can refer to Marriland’s Pokémon Scarlet & Violet EV Training Guides, which should help make your job easier by showing you which Pokémon to fight against to quickly and effectively EV train, although it’s up to you to decide which EVs and which Pokémon to use against Delphox.
After you’ve defeated it, you can catch it and you’ll be guaranteed to get an Ability Patch and TM141 (Fire Blast) the first time you defeat it. You can catch it only once; after that, you can still fight it again to get rewards.
This is the first of two runs of this event. Delphox (should) appear a second time the following weekend, from July 13, 2023 at 5:00pm PDT / 8:00pm EDT (July 14, 2023 at 00:00 UTC) through July 16, 2023 at 4:59pm PDT / 7:59pm EDT, although you can still catch it only once per game.