Suggested by Mike
Both sides are at their current incarnation, but gods (ie Khorne, Nurgle, Slaanesh, Tzeentch, Malal/Malice, Gork and Mork, C’Tan), ascended beings (ie Anubis, Ancients, Ori), or any daemonic entity not currently bound in some way on the material realm (ie Daemonhost, possessed vehicles/individuals, etc), though present in their current forms, may not take any active role in the match.
The battle takes place in a neutral universe. This universe has a merged timeline, and all involved galaxies converge onto one spot; meeting into a syncronized orbit of one another.
Both sides are made aware of the oncoming battle and are given 1 month of prep-time to develop strategies, but may not use this time to build new ships, or develop/adapt new technologies. Space-time manipulation effects are permitted, but jumping to an earlier point in time is not.
Which side wins?