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The Ghosts, not to be confused with Ghost from TimeSplitters 2's NeoTokyo, are non-playable enemies encountered in What Lies Below.

Their only attack is to float towards you until they make contact. The attack is a one-time deal as they perish afterwards. The danger lies in that they are invisible and are immune to practically everything.

The only way to harm and see them is through the use of a Ghost Gun.