Other known variants
x2
-20Insight
If you have the same number of cards in your hand as your opponent the attack cost of each of Yanmega's attacks is 0.
Linear AttackChoose 1 of your opponent's Pokémon. This attack does 40 damage to that Pokémon. (Don't apply Weakness and Resistance for Benched Pokémon.)
SonicboomThis attack's damage isn't affected by Weakness or Resistance.
If Pidgeot attacks with "Headwind" against Yanmega with the "Insight" Poke-BODY, will "Headwind" increase Yanmega's attack costs or will "Insight" reset them to zero?
If an Attack Cost is set to zero by an effect, it cannot be increased. Note this is different than an Attack Cost that was reduced to zero by subtraction. Once a Pokemon's Attack Cost is set to zero by an effect, it stays at zero until that particular effect wears off.
When Yanmega tries to attack, do you evaluate the number of cards in your hand for the "Insight" Poke-BODY before or after discarding a card for Giratina Lv.X's "Invisible Tentacles" Poke-BODY?
The Insight Poke-BODY is evaluated before your attack even begins; therefore it is checked before discarding any cards for Invisible Tentacles.