Duks pondered for a moment; his purpose here was Nightmare Dust, the more, the better.
The formula for the Pupil of the Rule Horizon demands extremely high purity of Nightmare Dust. The batch he collected himself was of excellent quality but not very large, just enough for a potion.
If he could have a bit more in reserve, whether for refining or backup, he would have more leeway.
More importantly, Nightmare Dust is a very rare resource even in the Wizard Plane and might be used later to exchange for other rare resources with other wizards.
He had no reason to refuse this proposal.
As for these Glowing Elves, Duke had no interest in harming them.
A group of thumb-sized Level 1 Lives posed no threat to him. Killing them would not bring any benefit, and instead would leave unnecessary traces in the Nightmare Plane.
Duks constantly remembered where he was and avoided trouble if possible.
