FINAL FANTASY XV MULTIPLAYER: COMRADES

This achievement is unlocked by defeating Gladio, Prompto, and Ignis. Each one will appear on their own at different intervals during the DLC, near the Power Plant. You will get notified of their arrival, so don't worry about not realizing they've spawned. Each time someone appears, go speak with them and agree to a fight. Once you have beaten all three, the achievement will unlock.

For Gladio and Prompto, you shouldn't have too much trouble beating them with normal physical attack strategies, especially if you took my advice from "One with Your Blade" (in the original FFXV achievement list) and crafted a really powerful weapon. Dodge and use a lot of warp strikes. For Ignis, he has a counter-attack that does a lot of damage and is difficult to avoid. If you have any decent magic spells, you can spam those and kill him without ever dealing with it, or just heal through it like the person in the video below.

Note: If you completed this achievement from the DLC version of Comrades inside FFXV (it was called "Royal Retinue Rumble" in that version) and transferred your character, it will unlock as soon as you spawn in Lestallum for the first time in this standalone version.