I didn't attend GenCon, but this whole chaining to the resolution of a chain has been around for several months since Kevin's first email regarding Snatch Steal vs. Magic Drain vs. MST. While there was never a public explanation, it seemed most people theorized out the whys of it. Creature Swap-CED really shouldn't be that radical after everyone got over the shock of the Snatch-Drain-MST.
I like the phrase of a response chain. I think that phrase could also work after the turn player performs a summon -- good way to explain priority (glad everyone finally believes priority doesn't just extend to the monster just summoned.)
So, here are some situations I could see and what is allowed.
Player A has a face up Shining Angel,
a face up Cannon Soldier,
a Breaker the Magical Warrior (which still has a token),
a face up Mass Driver and
a face up Wave-Motion Cannon (with 3 turns counted)
a previously set Burst Breath.
Player B has a face up Blue Eyes White Dragon,
a face up defense position Spirit Reaper,
a set Compulsuary Evacuation Device,
a set Mystical Space Typhoon,
a set Ring of Destruction and
a set Sakuretsu Armor.
Player A plays Creature Swap. Player B does not respond.
Creature Swap resolves, Player A getting Blue Eyes White Dragon and Player B getting Shining Angel. Now...
1) Can Player A activate Cannon Soldier to tribute Blue Eyes White Dragon before Player B activates CED? YES.
2) Can Player A send Wave-Motion Cannon to the graveyard to start the responce chain before Player B can MST it? YES.
3) Can Player A activate Mass Driver to tribute Blue Eyes White Dragon before Player B activates CED? YES. *Mass Driver never made the official priority list, but it certainly seems to work the same (an already face up spell speed 1 cost effect.)
4) Can Player A remove a token from Breaker to target and destroy one of player B's set Spell/Trap cards before Player B can Ring Breaker? YES.
5) Can Player A activate Burst Breath by tributing Blue Eyes White Dragon before Player B can activate CED? YES.
6) Can Player A activate Share the Pain (or any other spell speed one spell card) from their hand to start the responce chain? NO.
7) *IF* Makyura the Destructor had been previously sent to the graveyard this turn, can Player A activate Burst Breath from their hand and tribute Blue Eyes White Dragon to start the responce chain before Player B can activate CED? New scenario, but I would certainly reason YES.
8) Can player A tribute Blue Eyes White Dragon for a tribute summon to start the responce chain before Player B can activate CED? NO.
These are not UDE rulings and are certainly open for discussion here, but based on what we have today these make sense. (Key word being today.
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