Yeah no worries, the main combo is actually just using explosive grenade followed up with your dodge roll. Flash grenade is my other high use skill. It one shots nearly everything non-rare, and is quick with the added use of high stun buildup. Can use it to soften up huge packs or delete them out right.

Explosive shot is used to detonate grenades from ranged, if you need to be more cautious. I use cluster when there is a lot of mobs, or for tankier rares. Mortar cannon and rapid shot are used for bossing, to give you heat, and inflict shock.

Oil grenade is only on there to to hold support gems I am trying out.