These are the details as I remember them...
Bat Rep for Lucky 13's Apocalypse Megabattle May 9th at Comic Asylum in Garland, Texas USA
Forces of Order (8 players):
Howling Griffons SM with Whirlwind, Lascannon Predator, Vindicator, and Land Raider with Tactical Squad
Two Warhound Titans
Two Imperial Baneblade Variants (one with a Heavy Plasma Cannon)
A few squads of Nurgling Food
Smelldar including several tanks (Falcon Grav-Tanks I think), walkers, a few squads and Avatar of Khaine.
Forces of Disorder (7 players):
Ork Green Tide
Ork Mine Layer
Two Ork Stompas
Ork Gargantuan Squiggoth
Ork Pulsa Rokkit
Ork Deffkoptas Squadron
Angry Red Git Brass Scorpion
Traitor Hellhammer Baneblade
Kharne the Betrayer
Tyranid Barbed Hierodule
and my Nurgle force consisting of Lascannon Predator, Vindicator, two Dreadnoughts, and the dreaded Doomsday Device.
The offical GW scenario for this megabattle revolved around Ork Tellyportas and an Imperial HQ objective. You can find it at the GW site under the Lucky 13's Part One: The Menace Lands. The battlefield was packed with terrain, 6 Ork Tellyporta Pads and the Imperial HQ building, which dominated one end of the table.

Order bid 3 mintues to setup and deployed first.

They ended up having to bring some of their forces in as reserves because time ran out. Disorder, being chaotic and sneaky, decided not to deploy until Turn Two. Order, rightly mystified by our inaction, began targeting and destroying Tellyportas and terrain pieces alike. Volley after volley of Destroyer hits and Vortex Grenades left 85% of the battlefield covered in rubble by the middle of Turn Two. One Tellyporta survived, being in the Order deployment zone, but was unusable by Disorder as it was in Imperial control. The HQ building was firmly in Imperial hands as well.

One half of the entire Disorder force came in as reserves halfway through Turn Two, including the Brass Scorpion, Pulsa Rokkit, Mine Layer, Green Tide, Squiggoth, Kharne, Hierodule, my Predator, Vindicator, and the Doomsday Device. The Event Moderator let me bring the immobile Device 12 inches from our table edge due to special circumstances.

Our Shooting Phase went relatively well overall. We took out some troops and an SM Vindicator. Most of the SM in the HQ's upper level were destroyed by a Vortex Grenade, but miraculously, the HQ stayed intact.

The Pulsa Rokkit landed in the midst of a ruined building full of Nurgling Food and Smelldar...but didn't do much else that round.

My Doomsday Device just thrummed with power and sat there...my demand that the Order Forces leave the field immediately or suffer the consequences fell on deaf ears. The Mine Layer dropped a mine and shot some troops.
In the Assault Phase, the Brass Scorpion managed to eventually drop one of the Warhound Titans.

The Green Tide Waaghed in an attempt to get into the HQ, but failed. The Squiggoth and Kharne took out a Land Raider. The hero of the round was the Hierodule who single-handedly took out the second Warhound Titan, causing a Catastrophic Explosion that took out a good portion of the Green Tide, obilterated the Mine Layer, and caused wounds or loss of a structure point on the Squiggoth, Hierodule, and my Doomsday Device.
The top of Turn Three saw more Vortex Grenades, Destroyer hits, and general mayhem directed at the Squiggoth, Hierodule, my tanks, some Ork Nobs in a Truk, but remarkably not the Doomsday Device. The Squiggoth finally bit the dust, the victim of not realizing that the Force Field protecting the HQ actually should have been giving it a 4+ cover save all the while. Both sides are feeling the hurt a bit. My tanks and the Hierodule survive to fight again.
Finally, the rest of our Disorder Force enters the fray, focused on the HQ end of the table.

The Hellhammer, two Stompas, my dreads, and the Deffkoptas all come in on our table edge. Some Smelldar tanks buy the farm, courtesy of the
Stompas. IMG#9 The Plasma Cannon Baneblade is mauled by the Hierodule, giving up it's final structure point. The Doomsday Device remains powered but inactive. One of my Dreads rolls Fire Frenzy, but whiffs the rolls. The other one douses a squad of Howling Griffons with flames, taking out a couple.

My Predator gets a Drive Damaged result on the remaining Imperial Baneblade...which hasn't moved the entire game anyway. The Hellhammer takes out a few Nurgling Food. Ordinance blasts are scattering everywhere, taking out the final two ruins and the last Tellyporta. The Pulsa Rokkit emits an EMP-like blast that prevents a predator and some walkers from moving.
Our Assault Phase sees the Green Tide firmly in control of the HQ building. My one sane Dread assaults the Howling Griffons squad, and with the attached character whiffing his 5 attacks against me, I take one more marine back to Grandfather Nurgle.

They choose to fail the Morale check and fall back. This leaves me in base contact with a scout squad with meltbombs. Incredible rolls on their part leaves my poor Dread dead. The Brass Scorpion assaults a squad of Nurgling Food in some ruins, which leaves him open to attack by the Avatar of Khaine next round.
It's now the top of the final round, Turn Four. They toy with us a bit more, taking out the Hierodule's last wound. Khaine attacks the Brass Scorpion to no avail. They lob a Vortex Grenade into the HQ, taking out a few Orks. Finally they decide that they won't be able to retake the HQ and make the choice to destroy it. With that the battle ends in a Draw as does my hopes of seeing my Doomsday Device do anything of note. We had fun blowing things up and that's all that counts.
Chris