Felshield / Nibbles
Kystia takes reduced damage until Nibbles is damaged. At 20% he channels Destabilized.
Focus DPS on Nibbles, not Kystia. When Nibbles hits 20% health he turns friendly and channels Destabilized — pop every cooldown and burn Kystia during the damage amp window.
Officer tip: Do not ignore Nibbles to pad boss damage — Felshield extends the fight into more Mirror Images.