From Halopedia, the Halo wiki
The Blackguard armor is a suit of armor employed by the many clans of the Blackguard.
The Blackguard armors were implemented for use in Halo: The Master Chief Collection in Season 8: Mythic. The helmets are available for use in the Halo 3 and Halo: Reach components of the collection, while all other parts of the armor suite are only available for use as Halo 3 permutations.
The Flight preview builds for Season 8: Mythic contained an additional helmet that was later cut from the final release. The helmet, Blackguard Tearful Bishop, was featured in the original flight and given an official description in the accompanying Canon Fodder article released alongside the armours - though ultimately absent from the final release. The Halo 20th Anniversary celebration event in November 2021 ultimately saw a redesigned form of the Tearful Bishop, the Fallen Equerry, added into the game.
List of appearances