Robin Hood

Question : What happens if a player plays a card for free, such as with The Kadigir, Yzmir Bastion, while their opponent controls Robin Hood?

Answer : A free card remains free even against Robin Hood!
Playing a card for free means bypassing its cost entirely, which is different from reducing it to zero.

Question : Was this card updated ?

Answer : Yes. The first printing of Rare Robin Hood said
"Cards your opponents play cost more."
Future printings will say
"Cards your opponents play can't cost less than . (If they would cost less, they cost instead.)" This change impacts all versions of this effect, including the ones found on Unique cards. Any card that uses the previous wording should be read as if it used the new one.

Question : If I control Robin Hood, can my opponent reduce the cost of a card using an effect such as Martengale?

Answer : They can, but if this would bring the card cost under 2, the cost would remain 2.