 To develop a distinctive look for the various races of the Covenant , Bungie artists drew inspiration from reptilian , ursine , and avian characteristics . A Covenant design scheme of purples and reflective surfaces was made to separate the aliens from human architecture . The Covenant were generally well received by critics who appreciated the challenge they provided to players ; several critics lamented the change of the main enemies from Elites to Brutes in Halo 3 and conversely praised their return in the later Halo : Reach . 
