Here is an interesting situation I find myself in. I'm judging a duel between some friends of mine. One player has a dark magician with a sword of deep seated equiped to it. Then he activates diffusion wave motion. The oponent has 4 monsters on the field and a face down trap. The trap is Michizure. When he activates it, how does it resolve? Does diffusion wave motion kill one monster, then when Michizure activates, the opponents dark magician is destroyed before the dark magician kills the other monsters? Or is it something different?

Dark Magician would attack each of your opponent's monsters individually. You cannot use Michizure when a monster is destroyed in battle (you cannot activate Michizure during the damage step).

Michizure cannot be activated when a monster is sent to the graveyard as result of battle. The original wording on it was a little sketchy and has caused confusion in the past.

You can only activate Michizure when your monster is sent to the graveyard due to an effect, such as Tribute to the Doomed or BLS-EotB's effect.

So in your case its neither. Dark Magician can run through all the monsters and Michizure cannot be activated in response, unless there is something else to stop the Dark Magician 8^D

I see. They were working with the Michizure from Pharaoh's Servant which has the "error." Thanks for the clarification.