If Zoroark uses "Foul Play" to copy Reshiram's "Blue Flare" attack, what happens if I don't have have any Fire Energy attached to Zoroark?
The damage amount is done regardless of whether Zororark has any Fire Energy attached to it or not, but if you have one or two Fire Energy attached to Zoroark you must discard them.
Source: Black & White FAQ (2011-04-28), PUI Rules Team (2011-04-28)

Relevant cards

Note: All applicable cards may not be listed below.
BW1_71
BW1_26