Lorelei, or Heine as a companion, is a monster in the second part of Monster Girl Quest: Paradox.
Monsterpedia Entry
Attacks
Strategy
Evaluation
"You ended up as the mate of a high ranking mermaid... You stink of fish so please keep your distance. Lorelei is the highest ranking mermaid. Her techniques include White Magic, Ice Magic and Tsunamis. Since she is a mermaid, she is weak to Earth and Lightning. Binding, Blind and Paralysis are also effective so make use of those. Now go, oh Brave Luka. Have sex with birds and fish alike and conquer both the sky and the sea."