REKKR mod for Doom original can't be played in Doom II

I notice REKKR is a mod for the original Doom (1993), but when I attempted to load it into Doom II, it did load the assets with the Doom II levels. I got to level 4 when I noticed an NPC near the end is stuck and unable to be killed, so I was not able to go past it and not able to continue on with the game.

This happens at 9:03.

Otherwise, here is some information about REKKR:

REKKR is a total conversion mod for Doom, offering a unique and standalone gaming experience within the Doom engine. Here's an overview:

Gameplay:

- REKKR transports players to a Viking-inspired world, featuring new weapons, enemies, and levels.
- The mod provides a fresh narrative and setting, deviating from the traditional Doom aesthetic.
- Players explore medieval environments and engage in combat with creatures aligned with the Viking theme.

Features:

- REKKR showcases custom assets, including textures, sprites, and sound effects, creating a distinct atmosphere.
- The mod introduces new gameplay mechanics and enemy behaviors, enhancing the overall experience.
- It's designed as a complete replacement for the original Doom content, offering a different take on the classic game.