The Last Stand is a game mode that was added to Dawn of War II through patch 1.8. The Last Stand pits the player and two friends each in control of a single commander (Force commander, Mekboy, Farseer, Hive Tyrant or Sorcerer) against 20 waves of opponents that get more difficult as the wave number increases.
In order to reward the player for doing well their commander can level up through experience gained in the game. Leveling up does not increase the base stats of the commander instead it unlocks new wargear to make the hero more powerful or allow for different play strategies.
Wave 1: Ork Shoota Boyz
Wave 2: Eldar Guardians
Wave 3: Hormagaunts and Termagants (although if you actually play Warhammer then you will know that these are actually Devil or Deathgaunts not Termagants as the game calls them)
Wave 4: Imperial Guardsman, Force commander and two apothecaries
Wave 5: Termagants, Hormagaunts, Warriors
Wave 6: Shoota Boys, Nobz
Wave 7: Shuriken platforms, Guardians, Howling banshees
Wave 8: Termagants, Hormagaunts, Warriors, Zoanthropes
Wave 9: Shuriken platforms, Guardians, Howling banshees
Wave 10: Tactical marines with plasma guns and scouts
Wave 11: Shoota Boys, Nobz, Stormboyz
Wave 12: Shuriken platforms, Guardians, Howling banshees, Wraithlords
Wave 13: Nobz, Tankbustas, Shoota Boys
Wave 14: Termagants, Hormagaunts, Warriors, Raveners
Wave 15: Shoota Boys, Nobz, Stormboyz, Stickbommaz
Wave 16: Evil counter parts of you that are incredibly hard to defeat. They will use all the powers you own including such as a space marine dreadnaught and a hive tyrant warriors etc.
Wave 17: Termagants, Hormagaunts, Warriors, Raveners, Carnifexes and a Lictor
Wave 18: Deff Dreads, Nobz and a Warboss
Wave 19: Dreadnoughts, Tactical marines with plasma guns, Scouts, Terminator Captain.
Wave 20: A chaos lord will appear from a terminator statue in a cut-scene, summons bloodletters, your copies from wave 16 and will resurrect previous bosses like the lictor and warboss.