Wildermore Frost Grims on steroids?

Hi all <(")

I'm having trouble with the Frost Grims in Wildermore. At the moment, they're making it totally, and I mean totally, impossible for me to beat the final Wildermore instance (Final Stand). They do an absurd amount of damage to me, far more than any other creature does, and I'd be grateful for some help.

I'm a level 87 Guardian. The grims are level 85, non-signature. I'm totally fine with every other similar creature, but with these grims two at once will easily kill me and even one is a struggle.

Grateful for any suggestions posted here or messaged in-game (Guthir on Vilya).

Thanks!