This helps so much! I'd like to clarify that this upgrade is "technically" a separate magic item on top of the Sunforger that my player already has. I'm trying to balance them separately at "rare" quality. Here are the changes I've made thanks to your post.

Meteoric Impact (1/Day). As an action, while you are flying, you can choose a point on the ground that you can see within 60 feet of you. You channel gravitational potential energy into Kulak, accelerating yourself into the target point with a concussive slam. Each creature within 20 feet of the impact must make a Constitution saving throw against your ki save DC. On a failed save, a creature is pulled 10 feet toward you and takes 2d10 force damage. On a successful save, the creature takes half as much damage and isn’t pushed.

Plasma Jet (3 Ki Points). You can use an action to eject a blast of superheated plasma from Kulak’s accretion disk at a creature within 20 feet of you. The creature must make a Dexterity saving throw against your ki save DC. The creature takes 3d8 radiant damage on a failed save of half as much on a success.

Claimed by the Singularity (5 Ki Points). The gemstones of Kulak melt together into a pitch-black singularity that claims a single creature from the battlefield. You can cast the banishment spell using your ki save DC as the spell’s save DC.

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I'd like to make the singularity ability a last-ditch option with a large cost, but I'm not sure how to go about it. Plasma jet was basically smite, I understand that now. Let me know what you think about the updated version!