Ok, this is where I pour my knowledge about halo in. Jackals become Flood walkers that also transform into these things that shoot these spikes. Grunts can be used for those Flood carriers that explode when you get to near them. Hunters become huge things that still kinda look like hunters, just tan and diseased-looking. Drones, from fan fics I've read, are transformed in Flood dispersal pods. (don't know about the drone part for sure)