I had graviton for a while but I didn't really like it so I didn't use it for a long time then I was trying to get the immortal title and thought of it needed me to use void subclass then I could use graviton lance, I was wrong but anyways it is GREAT for like groups of thralls or vex goblins. Ex Diris is also great because first of all your using the gun that hive knights use which is already fire but now when you kill a combatant with it it will spawn a hive moth that's basically heat seaking and finds other enemies and kills them, plus there's no cool down, he only thing bad about it is it uses special ammo and can only hold 7 rounds at a time.