Unbearable Whispers - need help

How I can complete Unbearable Whispers IV prophecy on normal dif? Where should I seek this "certain powerful foe"? What type of monster this should be? Can't find him anywhere, There will be prophecy-themed quest thingy as soon as I will enter area with that monster or no? Please help...

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There will be prophecy-themed quest thingy as soon as I will enter area with that monster or no?

I don't think so, the tome will appear after you kill a perfectly normal rare monster, not something that spawned because of prophecy.

I slayed so much rare monsters already. I don't even know what to do now

You did it in normal? If you got the prophecy in normal you must complete it in normal (with a few exceptions).

Yes, I did it on normal.

Maybe it's bugged on normal then, the quest supposedly can be completed.

Just completed it. Act 1 Fetid Pool - Animal Skeleton monster.

Funny, I was heading to Fetid Pool, as I just got the prophecy, read this, took a portal to The Coast, was heading north looking for exit and saw an ornate strongbox. I decided to wipe out everything following me to roll it for the heck of it..and few golden/rare things were coming, I cleared them out and bam...prophecy fulfilled of Unbearable Whispers IV.

So in Short, completed this one on Act I, The Coast on Merciless.

I've done it several times and it spawns randomly. For me it was in random maps b/c I was doing maps. I assume if you are in the right difficulty it will spawn randomly wherever.

It's a funny prophecy that can randomly kill you in 6-man groups since the book will die slowly enough to do the crazy shocked ground-spark burst.