If I use Blaziken's "Inferno Kick Flurry" attack and my opponent has no benched Pokemon, do I still have to discard 2 Energy?
Yes, you do. The discard of the Energy is a separate effect and is not optional.
Inferno Kick Flurry




×2
Heat Blast

Inferno Kick FlurryDiscard 2 Energy from this Pokémon. This attack also does 120 damage to 1 of your opponent's Benched Pokémon. (Don't apply Weakness and Resistance for Benched Pokémon.)
When facing a tough foe, it looses flames from its wrists. Its powerful legs let it jump clear over buildings.
If I use Blaziken's "Inferno Kick Flurry" attack and my opponent has no benched Pokemon, do I still have to discard 2 Energy?
Yes, you do. The discard of the Energy is a separate effect and is not optional.