If I use Mega Lucario's "Aura Jab" attack but do not want to attach energy, can I choose to attach zero energy?
No, if you have any Basic 
Energy cards in your discard pile, you must attach at least 1 with Aura Jab.
Aura Jab
Mega Lucario ex
- Type
- POKEMON
- HP
- 340
- Energy Type
- Stage
- STAGE1
- Retreat Cost
- Weakness
×2- Regulation Mark
- I
- Rarity
- DOUBLE_RARE
- Illustrator
- 5ban Graphics
- Set
- Mega Evolution—Ascended Heroes (ASC)
- Number
- 113/217
Attacks
Aura JabAttach up to 3 Basic Energy cards from your discard pile to your Benched Pokémon in any way you like.
Mega BraveDuring your next turn, this Pokémon can't use Mega Brave.
Pokémon ex rule
When your Pokémon ex is Knocked Out, your opponent takes 2 Prize cards.
Mega Evolution ex Rule
When your Mega Evolution Pokémon ex is Knocked Out, your opponent takes 3 Prize cards.