The Combine are frequently shown as harsh rulers over the citizens of Earth, suppressing dissent with brutality, policing using violence and using invasive surgery to transform humans into either soldiers or slaves. Throughout the games, the player primarily battles transformed humans as well as synthetic and mechanical enemies that are the product of Combine technology. The atmosphere generated by the dystopian Combine state has been praised by reviewers, although the artificial intelligence of the transhuman Combine characters was thought to be inferior to that of other characters in Half-Life 2. In addition to their role within the Half-Life series, the Combine have been adapted for machinima productions and one Combine character type has been made into plush toys by Valve.