Doesn't really fit your description, but here was my first thought:
Fairy Ring - A ring of mushrooms sprout at the opponent's feet. Pokemon that switch into battle are inflicted with a random status effect.
Edit: raazychx posted...
A patch of mushrooms that grows around the tree. Said to give good luck to those who step in it.
An inverse of spike type move, it is for your team, and it gives HP when your pokes switch in.
What mythology did you read? Everything I've read says stepping inside a fairy ring incurs the fairies' wrath, which can range from really bad luck, to an early death, to being kidnapped and held captive in their kingdom.
"My faith protects me. My Kevlar helps." Michael Carpenter - Death Masks Official Norn of the Shin Megami Tensei IV board
Iron Maiden Type: Steel PP: 5 Power: — Accuracy: — Effect: The user lays a trap of piercing iron spikes around the foe. The trap hurts foes that switch into battle for 1/8 of their HP every turn. Does not effect Steel type and levitating pokemon.
If Steel types weren't already OP, they would be after this.
Electric Ring Switching in while this move is up causes floating orbs of electricity to link together and shock the pokemon that just entered, dealing a base 1/8 of the pokemon's max HP as electric type damage.
I only deal with 100% legit/uncloned pokemon in trades.