The Six-armed Serpent Demon fully exploited the information gap, catching the Necromancer Arms by surprise, wasting one of his precious spell-casting opportunities, and fully utilizing her physical speed advantage to close the distance between them.
As for short-distance teleportation, it wasn't that the Six-armed Serpent Demon didn't want to use it, but rather that she couldn't. This place wasn't truly part of the Material Plane, but a facsimile created with Negative Energy. It was detached not just from the Material Plane, but also from the Shadow Plane, existing in a gap between the two; without a victor decided between the two parties, not to mention short-distance teleportation, even plane teleportation was impossible.
In other words, this was a fight to the death with no way out for either party, only a path forward to the ultimate victory.
One wrong step and all would be wrong.
