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.

Relevant cards