The Final Nightmare

patron: "Sooooo .... sigh ... I have lost a bet and now I have to drink this one. Why is it called the 'Final Nightmare'?

barkeeper: "Well, if you manage to finish this, you won't have nightmares ever again! Fantastic, innit?" giggles maniacally

patron: "A little too good to be true in my humble opinion. There has to be a catch! What is it?"

barkeeper: "Oh, it is hardly worth mentioning. It will transform you a little ... a couple of tentacles here, an extra eye there, so ... ehem ... you'll be the star in the nightmares of everyone else instead. Pretty good deal, don't you think?"