From The TimeSplitters Wiki

Moxes are alien like creatures in TimeSplitters 2 and TimeSplitters Future Perfect.

(TS2) In story level "Return to Planet X" Meezor and Ozor moxes were in war. They fought against each other while trying to kill you either. Strangely, I don't know why there are moxes, because there was plain aliens while in planet x in TimeSplitters 1.

(TSFP) In Arcade league, league match "A Pox of Mox" You need to fight "Zones" mode alone against team of Koozer mox:es, and winning the match with any medal, you will open it as playable character.