This is a 2013 Halloween Contest entry. Please vote.
Father always warned me to avoid the fathomable places where mundanes may roam. I'm a wild creature and never heed. Danger excites me. Humans perversely intrigue me.
I've explored the threshold of my pond countless times. The orange red lances of fading light mesmerized me with reflections on the water. The moss and grass at the shore formed a comfortable nest.
I am Mercurial. That's my name or at least what I'm called. It suits me. I blame my namesake's capricious ingenuity for my love of surprises and trouble always courting me.
Surprises often turn troubling. On the thinning day when mundane reality touched the sublime world, trouble turned surprisingly delightful. Large hands snatched me, causing sudden staggering shock. I found myself face to face with a human. It was an ugly human. Well, they all are. It might be regarded as a pretty specimen of its kind. I'm not a good judge of such things.
Anger surged when the brutish creature's paws rent my gown without regard to the artistry destroyed. The beast was tall. Its hands encircled me in dull hide lacking any sparkle. It wore baggy clothes so ill fitting that hairs could be seen on its chest where a tunic draped. The creature employed a crude length of tanned leather to prevent its leggings from dropping to its ankles.
I struggled in the vice-like grip, but it was futile. Without heed, I slapped it across the face the way it deserved. The jolt of impact surprised us both.
"Ow!", it bellowed with the force of a gale.
"Beast!", I replied.
Pieces of my lovely tattered gown dropped from my sight. My rage and absence of fear disconcerted the human. It peered more closely, fending off my blows with one hand while holding me aloft in the other. My struggles accomplished nothing.
"Does this mean I get a wish?" The lumbering idiot croaked.
"That's leprechauns, you dolt. You won't like any wish granted by one of those fiends. You stay far away from their affairs if you know what's good for you."
"What do I get for catching you then?"
"You get to free me and hope I'm distracted before vengeance is opportune."
"I shall tote you in my bag and show you to my fellows?" it said. Actually, I can't remember the exact mode of anything it said in its strange slow speech. It meant something like that anyway.
Escape hinged upon return to my world before dawn. I didn't dare let the beast carry me away. Keeping the creature near the portal to my realm required enticement. If it remained by the pond, I intended to distract it or trick it into releasing me. Humans are none too bright. I had reason for optimism. I tried reverse psychology.
"You better not eat me," I warned counting on its ignorance of ancient law.
It scowled uncomprehending. "Eat you?"
"Don't deny your hunger for me. The scent of it betrays you." I pouted and fluttered my eyelids.
"Eat you - like roasted on a stick - with garlic?"
What horror was this? I was in worse trouble than I thought. I needed to turn its thoughts from that path at once. "No, dunderhead. Eat me like 'eat me out'. That's the most you're due, so don't think you'll get more."
"Huh?" The beast was not smart. 
"You know, eat me out? Your tongue between my legs? Cunnilingus?" I imagined the gears grinding out its thoughts. I couldn't risk any chance of misunderstanding, so I spread my legs wide and pointed. "Lick here."
 "You confound me, you wild creature," it said or something meaning that.
Subtlety never served me. I needed to pay the price without delay if I hoped to escape in time, so I shed the remnants of my gown revealing my sex for its inspection. At last, I had the beast's focus where I needed it.
My scent mesmerized the creature as expected. It had no idea who it captured. As a Naiad, my nature compels me to explore exotic interludes. As a daughter of Aphrodite, my nature compels lovers to serve me.
It tentatively nuzzled between my legs inhaling through the gigantic nose. The air current tickled, and I giggled enchantingly - exercising my power.
The tongue licking its lips extended to lick mine. Moonlight cast deep shadows hiding details of the face I didn't need or want to see. The thick wide tongue felt as large as my palm. It dragged against my flesh pulling slick folds until they stretched taught.