We had a total of 6 participants at last month's Game Day. Two Seraphon players, one Daughters of Khaine, one Tzeentch, one Slaanesh, and one Gutbuster. I used a slightly different variation of the Underdog rules from the previous Game Day, awarding bonus Laurels of Victory based on scoring objectives instead of for destroying enemy units.
This event was also my first test run for having the players interfere in one another's battles indirectly. The three battlefields were the Foothills of Koula, the Walls of S'nak, and the city of Regit-zharr. By scoring objectives at the Foothills of Koula, players could heal units on other battlefields; they could hand out Command Points by capturing the walls of Fort S'nak; and they could use the chaos duardin cannons at Regit-zharr to bombard other players. I think it was a pretty good success, and I plan to do more of it in the future. However, the cannons were a bit much, so I think I'll stick more to buffs in the future and see how that goes.
Slaanesh (led by Iradrüll) and Gutbusters (led by Lady Vendetta) ended up both going 2-0 (these events are only two rounds, so that we can be leisurely and also so that there isn't really much of a winner). It was kind of cool that it worked out that way since both of them were tied up in the narrative. So they decided to play an epic showdown battle later in the week. They fought within the mysterious labyrinth that the interior of the fortress had become, using some 1'x1' 40k Zone Mortalis squares of terrain. The Slaanesh player had the ability to spin the Zone Mortalis tiles, while the Ogors could smash them to pieces with hammers. It was a very cool and creative scenario that they put together. Anyhow, Lady Vendetta ended up accepting Iradrüll's surrender at the last minute, so they ended without a decisive victor, but with Lady Vendetta retaking Fort S'nak.