Mayong Mistmoore - once per server
http://wiki.project1999.com/Mayong_Mistmoore
SK/EK Ancient Cyclops - never seen it on live or P99 and spent hundreds of hours tracking in SK.
I remember on live early on there were tales of a Kraken in Ocean of Tears or Lake Rathe (I've heard both). Below is a rumors thread that mentions that it might have been in beta but no screenshots exist.
http://www.project1999.com/forums/sh...d.php?p=112743
Also in that thread it mentions "Nightmare" a level 20 horse in Lavastorm. Don't think I've ever seen him either.