Bosses are large, powerful enemies that must be defeated to progress. They appear at the end of each mission in Blake Stone: Aliens of Gold, and in levels 5, 10, 15, and 20 in Planet Strike. Defeating a boss allows the player to obtain the access card needed to progress further and complete the mission. Planet Strike adds 5 new bosses, while the bosses from Aliens of Gold re-appear as regular enemies.