Iron Plague is the official expansion to Total Annihilation: Kingdoms. It introduces the fifth faction, the Creon, created by Garacaius during his absence from the land of Darien. The Creon are a steampunk-styled faction which relies on mechanized units instead of magic. Their monarch, The Sage, wears a heavy steam-powered suit and one of his attack types has a long range, but he is the only monarch in the game without a special ability.
The expansion pack also includes 25 new single-player missions and 25 new multi-player maps, as well as previously downloadable content for the base game, including official patches and units, as well as The Darien Crusades, a co-operative multiplayer mode whose balance settings can be applied in standard skirmish and multiplayer matches.