You must clear the stage 12 first then, At the end of Scene 4 notice the two doors (one
on the left and one
on the right) on either side of a center barred door. Go through both doors and complete
the
ensuing scenes. After you completely open the door to the boss head back to the beginning
of
the stage. On your way you notice a Balor Danu. Kill this to open the gate back towards
the
beginning. Go through this and continue to where the Thanatos Chip sits (in the room
behind the
gate). Defeat the spawn of Verge Guidodagda and the gate will drop allowing you to pick up
the
Thanatos Chip.