When the selection of the two attributes by the owner of Earthshaker and the selection of one of the two attributes by his/her opponent is done, at activation or at resolution?
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Answer:
The player that activates "Earthshaker" will not name 2 Attributes until the effect is resolved.
When "Earthshaker" is resolved, first you declare the 2 chosen Attributes. Your opponent will then select 1 of the 2 Attributes and then all face-up monsters with the Attribute your opponent chose are destroyed.
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Does the oppenent need to have at least 2 face-up monsters with different attributes for the other player to active Earthshaker?
Answer:
Actually, no.
All "Earthshaker" needs to activate legally is one face-up monster on the field. When "Earthshaker" is resolved, the player that activated it declares any two Attributes they want. They don't even need to declare an Attribute of monster(s) on the field.
If your opponent only has a WATER monster and you declare WATER and DARK... well, they probably won't pick WATER, will they?
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Curtis Schultz
Official UDE Rules Dude
CurtisSchultz_Netrep@Hotmail.com