There are two main facts that are crucial to this build:

1. Radiation damage does not apply confusion to affected targets, but rather disrupts the insulin production in their system and forces their compatriots to mercy kill them before diabetic coma sets in. It has been shown that exposure to ionising radiation is linked to higher chance of developing a chronic metabolic disorder, such as Type II Diabetes.

2. Eidolons don't have any goddamn Islets of Langerhans.

Therefore, while the [Kuva Chakkhurr], especially when modded with radiation damage, is highly effective at getting enemies to kill each other out of compassion, it is even more effective against Eidolons due to the gun itself being essentially a giant candy cane.
As Eidolons are unable to produce insulin (at least in effective amounts) but do have some sort of circulatory system (evidenced by bleeding after you destroy their synovia), they effectively have Type I Diabetes. Thus, the forceful addition of sugar from the Candy Cane of Death straight into the bloodstream is a highly effective method of shifting the Eidolon's homeostasis rapidly towards lethal hyperglycemia. Should the Eidolon be capable of any insulin production, the radiation element would serve to disrupt it, though this may not be an outwardly visible symptom. Once diabetic coma is achieved, despite the delivery of supplementary insulin to the Eidolon by nearby Vomvalysts, it can be safely captured by your lures and violently dismembered to grant you the arcanes you were willing to commit medical malpractice for.

A riven is not required, but improves the sugar load forced into the Eidolon with each shot. Raw damage, relevant elementals, and critical damage are the ideal positives. Radiation bonus damage is best, so get the correct candy cane from your local Lich™ retail store.

Features:

• Fun for the whole family squad.
• Can be painted green and red for Christmas time.
• So hard you can beat people to death with it.
• Also good against anything else with a bloodstream, and also for some reason robots. Working theory is that the sugar has nothing to do with this, and the radiation just fries their electronics.
• Very handy for a quick snack, or for breaking your teeth.
• Once you get used to leading your target, Ammo Drum may be a better choice than Terminal Velocity.
• Arcane Acceleration does help with more rapid injection mechanism.
• Can still headshot in the final phase of blood sugar imbalance, bypassing the blood-brain barrier.