Please watch for updates.

In the mean time, read the various victory reports for some insight vs Laz and Diablo.

See also, Laz's Chamber inside the Firewall Guide.

Laz’ Chamber need not be feared if you know where the monsters are. The pic shows where everyone is when undisturbed. Note that there are always 4 doormen in Laz’s chamber and the first one on the right is on the first row immediately inside the chamber, second one on the right is on the third row. The first one on the left is on the second row, and the second one on the left is on the fourth row.

You can approach the chamber opening from as far South as the layout allows, then stop at 3 tiles away without activating anyone. Now, just lay four rows of Firewalls inside the room where the Advocates are. Listen for the sound of Advocates roasting and dying, recast if necessary. Although I would not recommend it (there are better ways to activate them one at a time), you can also fry and activate the 2 unique witches while the Advocs are roasting. Still standing at the same spot, you can see the top of the cool design (four pointed star) on the extremely top left-hand corner of your screen. Casting a Firewall there will activate both witches.

The preferred spot to kill Diablo is at one of the corner of the two-lever room. That corner spot offers many advantages, 3 of them being: (1) It’s easier to control where Diablo will stand. (2) Player(s) don’t get knocked back and therefore keeps Diablo in the fire. (3) Mage (and the rogue) standing around the corner will not be attacked by Diablo’s Apoc. When the warrior and Diablo is set at the corner, the mage can cast the Firewalls on big ugly and still out of his line of sight and attacks. The mage and rogue can now move into the sniper position to give the warrior a hand.

Another big advantage of using the corner is that you can stack more Firewalls than the normal sprite limit would allow. Normally, this translate to 11.5 Firewalls to be cast (11 flames x 11.5 = 126.5, close enough). But not every Firewall uses up 11 flames/spirit, when casting around the corner it will only allow 8 flames for each Firewall so you can stack almost 16 Firewalls. And. if the party feel confident enough to have the mage standing next to the warrior at the corner, the flame count per Firewall would go down to 6 letting you stack the Firewalls 21 deep - that’s virtually doubling the damage or half the time needed to kill. This may sound obvious but for the sake of those who doesn’t know already - stacking Firewalls (placing FWs on the same spot) multiplies the damage done by the amount of Firewalls stacked.

From Posts

Diablo trick - Morgane - Thread
I developed this tactic as a means of killing Diablo in Varaya & Khan Hellfire with as little risk as possible to the characters. The incentive was The One Ring which could only be obtained by killing him. Because he's stronger in Hellfire than in Diablo, and I believe stronger still in V&K Hellfire, my characters were usually just a nubile 18th lvl when they'd reach his lair for the first time and so needed a safe and effective way of dealing with him.

This is a variation of the familiar "cast lots of firewalls in front of you while dueling Diablo". In this case the wall is between you and Diablo instead of at your back. The wall protects you from any Apocs and Melee attacks he may launch.

1. Find a long wall in Hell that has a safe side where you can wait out Diablo's death throes.
2. Cast Firewall (as many as you like) against and parallel to the wall. Do this on the side opposite the one where you will wait.
3. Summon Diablo with a Charged Bolt or Lightning etc. I like CB because it travels slowly and gives me more time to escape.
4. When you are sure you have Diablo's attention, teleport over the wall and wait on the other side, pressed as close to the wall and close to Diablo as you can.

What should happen is Diablo will start looking for you and try to get as close to you as he can from your last known position - which is where you teleported to, as the game is aware when you cast a spell. Diablo will move up and down the wall trying to get around it and reach you. He'll travel about 6 squares in either direction. Meanwhile he is running back and forth, up and down through the length of the Firewall. If you think he gets exposure from just standing in a multiple Firewall, wait until you see him run through one!

Why does this kill him so quickly? Because a creature moving in Diablo spends a bit of time in 2 squares at once, and will automatically be hit by anything affecting either of those squares. As you can imagine, when you have a lot of Firewalls, that's a lot of 'being affected'. ; )

I used to use Stone Curse, Infravision and a lot of stealth to execute this tactic inside Diablo's Chamber. But because this tactic is cheesy and exploits AI and spell bugs, I don't use it very often any more, usually just for a laugh. : )