Based off of the Pokemon Stadium stage series from the SSB series. I did modify it singificantly, though.
Arena: Pokemon Stadium
Type: Varies
Comlpexity: Medium
Restrictions:
Unless otherwise mentioned, the following are in effect always:
No sources of anything
No siesmic attacks
Digging is allowed.
Description:
Pokemon Stadium can change between types quickly. At the end of each round, it has a 75% chance of changing into any other arena type.
Moves matching the arena type have a 10% greater final damage (after all effects of items, abilities, moves, etc.)
Moves of the type the the arena type is weak to have a 10% lesser final damage.
When the arena changes types, it will change to each type with equal probability (including the one it just was).
When the arena changes types to one with a certain weather, that weather will be in play, barring weather changes, until the next arena change, where it becomes no weather.
Normal:
Nothing special
Fire:
Fires are burning. Pokemon will get burned if they hit the fire.
The weather is always harsh sunlight.
Water:
The arena has lots of water.
A river dumps into the arena, creating a waterfall.
Rain is always pouring down.
Grass:
Grass sources exist.
Trees that you can hide behind exist.
There are a few hills to hide behind.
Solar rays are always flooding downwards.
Electric:
High voltage wires with no insulator are running across the arena.
Any pokemon to touch the wires gets hit by a 4 BAP, increasing by 2 each action it stays on the wire, STAB electric-type move from a Special Attack of 4.
Torrents of water are always rushing from the sky.
Psychic:
Psychic powers are much stronger. As such, limits or damage reductions (barring type effectiveness and stat stages) on psychic-type moves are lifted.
Ice:
The arena is made of pure ice.
It can be melted with Fire to make water, which can then be used for attacks.
It is constantly hailing.
Dragon:
Base Rank differences matter twice as much.
The arena is very warm, so ice melts and ice-type moves become water-type ones.
Dark:
Effects inflicted by moves (paralysis, attract, sleep, etc.) are twice as likely to have effect. Effects like sleep last twice as long.
Fairy:
Moves deal 75% normal damage (82.5% if Fairy, 67.5% if Steel or Poison).
Fighting:
Just a flat arena, stretching into infinity, with no special anything.
Seismic attacks are legal.
Flying:
Strong updrafts to make moves that involve flying upwards (fly, sky drop, etc.) have +1 priority.
Poison:
Covered in toxic sludge that poisons all pokemon, barring those immune to poison.
Ground:
Seismic attacks are legal.
Limited ceiling.
Either a sandstorm or bright sunlight, with equal probability, are happening.
Rock:
Giant rocks are scattered everywhere.
A sandstorm is always going on.
Bug:
It has a 50% chance to rain.
Each pokemon's stats are subtracted from 10 to get their new stats in this type (base rank 11+ still means new base rank 0).
Ghost:
The arena is a maze with a limited ceiling.
Ghost-types can move through the walls.
The walls can be dug through, but the floor can't.
Steel:
The arena is made entirely of steel.
It can not be dug through.
Rain is always flooding down.
