After D.D Warrior Lady designates my White Magician Pikeru as an attack target, I activate Magical Dimension. I tribute White Magician Pikeru and special summon Dark Magician from my hand. I can then destroy 1 monster on the field.

I do not destroy D.D Warrior Lady. Instead I destroy Marauding Captain.

Since White Magician Pikeru has been tributed, D.D Warrior Lady has lost her target. Can D.D Warrior Lady designate a new target when this happens? Can she attack my Dark Magician?

Yes D.D. Warrior Lady gets a new Target because the number of monsters had changed. Then your opponent can attack again, which ever monster he/she chooses.

Yes...cause it caused a replay...simple as that...since the number of attack targets on the defending player's field (your field) changed (from 1 to 0 to 1)...the attacking player has the option of selecting a new attack target or not attacking.

Going from 1 to 0 to 1 again has nothing to do with this.

The fact that the attack target has been removed from the field is the sole reason why, in this scenario, a replay would occur. Another way of looking at it is that a new "defender" has been put into play and the turn player may choose a new target if they so choose.

Actually, it does...because the number of attack targets has changed on the defending players field. 1 to 0 to 1 is how it changed...though the 1 to 0 is sufficient.

Why is a replay triggered when I activate Magical Dimension? The card text says "Tribute 1 monster on your side of the field and Special Summon 1 Spellcaster-Type monster from your hand." The number of monsters on my side of the field has not changed.

Cause you're the defending player and the number of attack targets on your field changed when you used Magical Dimension.

Assuming White Magician Pikeru was your only attack target at the time, by using Magical Dimension, you changed the number of attack targets on your field from 1 to 0 after tributing and then to 1 again for the Special Summon. Regardless of how many there are in the end, it still changed, thus causing a replay.

White Magician Pikeru is tributed the moment Dark Magician is summoned to the field. The two effects resolve simultaneously. Since there is no time between tribute and summon, the number of monsters on my side of the field does not change.

Umm...Yes it does...regardless of WHEN it happens, it still changed...it STILL went from 1 to 0 to 1 "at the same time" as you put it.

A replay does occur, in that we both agree. I just wanted to get that out of the way now so that we can keep things in perspective.

The number of monsters being changed in this scenario is not the main reason why a replay occurs, the initial target of the attack is no longer there . . . so what is the monster going to attack if it's target is no longer legal? It doesn't know unless the player chooses a new target. What it boils down to is if the number of defenders change OR if a/the defender is no longer on the field before the beginning of the damage step a replay will occur.

Yeah, pretty much we're both just saying a replay still occurs, lol

Yeah...we know the whole replay occurance thing, just talking about numbers and all.

thats why i still think the wording for a replay should be fixed to say what it actually means.

"a replay occurs when the number of monsters on the defending player's side of the field changes" just doesn't cover everything. it doesn't cover effects that may or may not allow a direct attack. and there will always be people like judgex who refuse to accept 1 to 0 to 1 as a change.

it should be more like what shadowsetokaiba said. "a replay occurs when a potential attack target is no longer legal or if another becomes legal." or something like that.

It's not that is "should be" what Seto said. It IS what Seto said. If a potential attack target appears or disappears, there is a replay. Even though numbers changing is a side effect of this, the way it is enforced and determined, and ruled on the judge's list by TPTB is what Seto previously said and what I repeated. A potential attack target appearing or disappearing. Duelists would be best served by not referring to numbers at all, as you folks were doing earlier in the thread.