This schematic is located in the Halondrus boss encounter area in Sepulcher
You must complete The Final Song in order to see the Schematic, as you do all other Mount Schematics.
Can be found by one of the gate things on the room where the second phase of the fight happens.
Pattern doesn’t spawn until you kill the boss, so you’ll need to join a group, kill the boss, and then run back to the second phase’s room to loot the pattern.
LFR works
If you reset the raid in any way, the walls that separate Halondrus’s rooms go up again, so this pattern becomes unreachable on that lockout.
/way 63.18 51.92 in the 2nd room of the boss encounter after the boss was dead.
None the Wiser Guild 