There is 1 Dead Ghost to be found in Asylum. They can be collected on any match mode. Each Ghost can only be collected once per account.
Once again, this found by one of the starting spawn points in the map. Head into the marked door and go to the left toward the closed end of the corridor.
Head into the very back portion of this corridor. On the ground, to the right of the DWT sign, in the grass you will find the Dead Ghost.