Mind Games is an achievement in Halo: The Master Chief Collection. It is awarded for activating the ninth Halo: Combat Evolved Anniversary Terminal on Keyes. The achievement is worth 5 gamerpoints and can be unlocked on any difficulty.
The ninth terminal is found beneath the Proto-Gravemind, in one of the sunken crevices to the side of the raised platform. The terminal is a red holographic panel, and is on the wall of the right crevice.