now, while brutal kills should be brutal. lets not get too carried away. some of these sound like they could take a pretty long time to play out.
anyway, not sure if you guys are thinking of your brutals to start differently but for mine theyd all start with the good ol tether punch to the face (one that knocks em back but theyre still on their feet facing you)
Ares: fire punch through the chest and as he withdraws his hand they incinerate into ashes
Hades: a portal opens underneath them as a hand reaches out and slowly drags them down while you tear out their soul. you finish ripping out their soul about half way done so the portal closes cutting them in half at the waist leaving only their torso and up left as you absorb the newfound soul youve claimed
Poseidon: freezes the opponent and summons a portal for the kraken to appear through and devour them
Zeus: lifts them by the face and sends lightning currents throughout the body until it is fried beyond recognition. then just tosses the corpse to the side like its nothing