We have a couple issues the flood may encounter. The flood are from the halo games which were made by bungie. -the taken and those who control them(could the flood infect a taken, or would the spores die trying this. Or could spores be taken.) - ascendant realms - siva - gaurdians and the ghost (could the ghost prevent the flood from controlling a gaurdian? Resurrection. -the light -the darkness The factions that could run into trouble are.. -The fallen except for servitors and shanks? -The cabal -The vex maybe (they have alot in common with the flood) could the flood be turned into vex like kabr in vog. I don't know about the scorn or hive being infected.