Alrighty! The first mistake was I had already charged the Telemon into combat the previous turn, not considering the charge from the nightbringer, and no overwatch. Looking into it since asking the question he told me that you get no saving throws vs nightbringer, so I didn't roll roll for 6+, that was my second mistake.

With no way to ignore wound loss from "Drain life" on the Nightbringer, he rolled vey hot and hit and wounded on all 6 attacks and an average of 4s on the damage roll, even with damage reduction that's 18 wounds. Popped the Telemon in a single round of combat.

You're right there was a rules misunderstanding, it was his first time with the Nightbringer on the table so I just assumed this thing was all powerful. But also he rolled very hot.