The gem started to shine of a white light, which started to pulsate. It then halted its light and the gem seemed to be back to normal and its effects gone. At first, at least.
"Er... Is it supposed to do that?" Mark stammered, nonplussed.
"No... The vendor at the store never mentioned that, honest," you answer back.
"It's fun, though," Mark smiled. "I wonder how it works exactly."
He was about to examine the necklace at a closer angle and discover how this piece of jewellery functioned. There were no mechanism he could see but he let go of the necklace quickly as if he'd been burned.
"What’s the matter?" you ask, suddenly worried.
"I... I don't feel well..." your friend stammered.
You want to go get help, unfortunately Mark gets very dizzy and he starts to loose his balance. You steady him and get him to sit back down. You get frightened. Did he drink too much? Did someone slip something in his drink? Or worse, did he take the drugs? You didn't care about the legal repercussions, if you have to take him to the hospital and he did underage drinking, at least he'll get help and not die of an alcohol-induced coma while being left where he lied, passed out. As these alarming thoughts swirl through your head, you see changes that stop you dead. Changes that certainly no hospital will know what to do with. And you even start to wonder if you haven't taken drugs inadvertently yourself. Mark starts to cover himself with hair. Light brown thick hair. His ears elongated and became covered in tufts. Mark scratched his new body hair, mumbling that it itched. All of a sudden, he moaned and groaned. No wonder: horns sprouted from his higher forehead, thick horns with rounded tips. He continued his groans and moans and he then acted very oddly indeed. He kept muttering that he was hot, so very hot and he actually removed his clothes. His shirt first, revealing chest hair that had transformed themselves into that same thick fur. Then his shoes and pants, even his boxers. His legs bent more at the knees and twisted outwards as his ankle structures moved upward. His toes and nails fused and hardened, turning into big cloven hooves. The last and most frightening and disturbing change arrived at his groin. Mark's pubic hair had already been replaced with the same thick yet soft-looking fur. But his privates bulged and a panting and sweating Mark stared with awe, fascination and terror as his penis elongated. It throbbed, twitched and his testicles enlarged considerably as well. Already it was standing erect and the pre-cum dripping demonstrated how much it demanded attention.
"Mark..." you whispered, unable to comprehend the reindeer and human and hybrid in front of you. The reindeer satyr turned to you, with a small light of recognition in his pupils, which was extinguished as the fire of lust took him over. He was overpowered by the desire of the flesh and it was clear he could not think of anything else. He was now a slave to his own carnal desires. And he had every intention of knowing you - in the biblical sense of the term.
"Susan... You are so pretty... So enticing... I want you... Now... I can't wait..." he panted, all to his pursuit of the flesh.