Heroes of Might and Magic III: Armageddon's Blade (lost beta build of expansion pack for turn-based strategy game, 1999)
From The Lost Media Wiki
Technically, the beta builds of Heroes III have never been found with only screenshots and a few pre-release footage available. However, the first expansion pack Armageddon's Blade has had an infamous development history with the proposed Forge faction, that lead to negative feedback by fans, resulting in Forge being cut in favor of the Conflux faction. As of today, the beta build for Armageddon's Blade hasn't been found like with the Restoration of Erathia beta builds.