If I have no Benched Pokemon and attack with Tornadus' "Hurricane", do I have to discard an energy?
No. If you have no Benched Pokemon there is no place to move an energy card, so you would not do that part of the attack.
Source: Emerging Powers FAQ (2011-09-01), PUI Rules Team (2011-09-01)

Relevant cards

Note: All applicable cards may not be listed below.
BW2_89
BW2_98