Order of the Phoenix/Death Eaters versus the Mutant Brotherhood....
The members of the OOTP and the Death Eaters happen upon the Mutant Brotherhood as the Brotherhood holds it's meeting in the woods.
OOTP/Death Eaters:
Voldemort
Dumbledore
Bellatrix Lestrange
Fenrir Greyback
Nymphadora Tonks
Mad Eye Moody
Kingsley Shacklebolt
Remus Lupin
Sirius Black
Minerva Mconogall
Lucius Malfoy
Sirius Black
Severus Snape
Dolores Umbridge
The 4 Death Eaters from the OOTP movie, and the two from the opening scene of THBP.
(I think I got them all, if not, let me know)
Scenario one: Working as a team, the wizards decide to kill the Brotherhood.
The Brotherhood is aware of the attack a minute or so before it happens, and it is night.
Scenario two: Same as one, except that Dark Phoenix is there, and Voldemort has control of the Dementors.