For the Love of Mother
This is your showdown with Mordred. You are now in the upper tower of the Castle of Sorrows, and you must hunt down Mordred, while thwarting the specialized guardians that are protecting him. This is an extermination level, so you must kill every enemy in the level, including Mordred, and then recover the grail.
Walk down the corridor until you see a flag on the right wall of Morgana
Flip the switch behind the flag which opens a nearby door to a platform
Take the platform up to a hightech area, flip the switch on the right to activate power, then flip the other switch to open the door to the barrel room
Take the platform back down, and enter the next room (which is the barrel room)
From a distance shoot out the barrels, then walk up to the Morgana wall and hit the action key to begin descending
At the bottom of the platform, flip the switch on the wall, then proceed up the stairway past the lava pit and up to the Mordred terminal
Jump down the hole into a room, then exit that room back out into the main hallway
Take the hallway back to the platform up to the hightech room, and the door in that room is now open
Jump through the door into a private dining area, and open the secret door where you see an image of Morgana on the wall
Take that room to a stairway which leads down to a well, and jump in the well
You are teleported to a hightech room, flip the switch and enter the holodeck textured alcove to teleport to a stairway near Mordred
You're already at the top of the stairs, so follow the red corridor until you reach a 2x recharge
Walk through the corridor of armor into the domain of Mordred (the walls close up behind you)
Use the two stairways to fight the Black Knights in the room with you (climb up, shoot, jump off, run to the other side, climb up, shoot, etc)
When the Black Knights are dead, flip the switch at the top of one of the stairways to reveal a control panel
Walk up to the control panel, and Mordred will come out to fight, so immediately run back and enact a strategy of killing him
Once dead, pick up the key he leaves behind, enter the area behind the control panel and climb the stairs around the lava
At the top of the stairs read Mordred's poem, use the key to unlock the door, and enter Mordred's room
Read the terminal in the room to exit the level (if you left anyone alive, Merlin will tell you so and teleport you to the ledge outside the tower, so you'll have to flip the switch and re-enter the tower, hunt down the rest, then re-enter Mordred's domain by way of a new passage that opens up)
To Kill: Mordred, 2 black knight Guardians, 1 standard black knight, 3 shadow sorcerers, and 8 archers
Eye Candy / Extras
At the start, do not shoot the barrels next to the door or they'll explode in your face
If you continue down the corridor past the well, a passage will open up which leads back out to the main hallway
When you pass the lava pit where the shadow sorcerers attack, you can jump across the lava into cave passage which contains missile ammo
After passing the lava pit and jumping into the room with the barrels, shoot the barrels to grab some water vials, and check the lockers for some health potions
There's also a lot of water vials around the well, but that's pretty obvious
Look through the window past the Morgana flag, and you can see the switch outside the tower, shoot the switch and you can gain access to the outside ledge where you'll find some hightech plasma ammo