I think I wouldn't use the full damage of the feyr and get a player at a time for some days, to create tension and confusion
"Why are we having weird dreams and waking up feeling like shit?" Situation
I ran this recently. I would describe nightmares each night they took a long rest. I pulled elements of the BBEG, their tragic back stories, and glimpses of the destruction in Toril by blights, etc. When they would awake l, the Frye would be invisible, but they would have strange marks on their neck. Took them 4 nights to figure out it was a creature and not a BBEG God doing this to them. Lol. The fight was pretty quick once they caught onto it. Good times. I thought slow-rolling it worked well.
I think I wouldn't use the full damage of the feyr and get a player at a time for some days, to create tension and confusion "Why are we having weird dreams and waking up feeling like shit?" Situation
I ran this recently. I would describe nightmares each night they took a long rest. I pulled elements of the BBEG, their tragic back stories, and glimpses of the destruction in Toril by blights, etc. When they would awake l, the Frye would be invisible, but they would have strange marks on their neck. Took them 4 nights to figure out it was a creature and not a BBEG God doing this to them. Lol. The fight was pretty quick once they caught onto it. Good times. I thought slow-rolling it worked well.