I'm guessing that the environment started changing when the Artefact Core Fragment crashed over Neviwind Canyon.

I still don't know exactly what kind of power the Fragment possesses, but it's clear that it's influencing the creatures here.

This is proven by the mutated old creatures showing up at the Remnant Altar and in the Jotun Garden.

I'd like you to kill Secretive Kaisan or Murky Bagatur and then report back to Skamish.
You mean you killed the Mutated Old Creature[pl:"Creatures"] and obtained helpful information in the process?

Although the Core Fragment changed it, didn't it receive the power of the Artefact?

We have to hurry and gather the Artefact Core Fragments before the Elyos get the jump on us.
(You clicked on Instant Report[pl:"Reports"] in the Quest Journal and reported about the mission.)

(Click 'Confirm' to receive a reward.)