He’ll probably primarily use his energy sword with a healthy dose of plasma grenades on the side. In game (Halo), the energy sword is a high damage weapon with a huge lunge attack that launches the wielder toward his target from 3-5 meters away (depending on the iteration) for an instant kill. Obviously damage would need to be toned down for a fighting game, but I imagine it will fill the same role; high damage mid screen lunges. He might also be able to have an uppercut version that launches him skyward.
Plasma grenades would function like Cinder bombs, but if they function like they do in Halo they’ll have a set timer and do high damage.
Also prevalent would be his Elite Power Armor, which provides both a recharging energy shield (he’ll probably have armor in some situations like Aganos and Glacius) and Active Camouflage (temporary invisibility, probably like a better version of the effect provided by Fulgore’s teleport)
I’ve actually got a whole thread on this with details. I’ll just do the selfish plug.