There may be two forms of the word, the mythical creature and the Internet "troll" who spreads anger and discord through anonymous online forums. I am interested in the second form of the word, though the first form might be interesting, too.
This word is borrowed directly from English and it's actually "тролль" or "троль" (pronounced almost like English
trol but l is softer). It's quite common word in Internet slang and there is also a verb derived from it -
жирный тролль (zhirnyj trol`, literally a fat troll) - about somebody who is, well, let's put it this way, a dedicated, passionate troll.
As of palatalization (the way final "l" is pronounced softer) it's not easy to pronounce for someone who is a native speaker of a language where there's no such thing. But you can try to pronounce
trollee and than try to pronounce
ee very quickly, as quickly as possible. And then even shorter :)
A sidenote - "original" troll is also
тролль in Russian (since its a Scandinavian word both in Russian and English) but actually there's a theory that English trolling was initially based on the concept of trolling - a fishing technique, and only later this word became associated with mythological creature. More about it.