Items:
Melt Stone
When the Pokemon holding this item enters the field, all foreign objects are destroyed. Any non-Fire type Pokemon takes damage when switching in with this item.
By 'foreign objects', I of course mean entry hazards, Light Screen, Reflect, Safeguard, and Substitutes(Probably others, though I can't think of any right now). The way I see it now, this removes such things on the user's side as well as the opponent's.
Swarm Stone
When the Pokemon holding this item enters the field, all foreign objects are carried away. Any non-Bug type Pokemon takes damage when switching in with this item.
Gust Stone
When the Pokemon holding this item enters the field, all foreign objects are blown away. Any non-Flying type Pokemon takes damage when switching in with this item.
Blizzard Stone
When the Pokemon holding this item enters the field, all foreign objects are frozen and crumbled away. Any non-Ice type Pokemon takes damage when switching in with this item.