Map of Killbug's approximate spawn point (Click for full map).
The player must have spoken to the "Huntmaster" in Phon Coast and defeated Thalassinon to start of the Rare Game quest. Killbug is then found on the Switchback area of the Ozmone Plain on the northern edge near the entrance to Zertinan Caverns when the clock is between 10 and 39 minutes. It is easy to spot as it does not match any of the other treasure chests found on the plains, and is larger than usual. This enemy a Trophy Game, and thus can never be found again after having been slain.