Imagine this situation -
Bob's board: Charming Prince, 8 life
It's Bob's turn. If Alice gets to attack & pump, Bob is dead (Charming Prince can't block Steel Leaf Champion because of the Champion's ability). Bob is holding a Gideon's Reproach, so he's technically not going to die this turn - if Alice pumps, he wins the stack battle with the Reproach. However, Alice is skilled enough to play around Gideon's Reproach, so he's still going to die in two turns and his back is against the wall.
Bob comes up with this plan:
- Although Alice has no blockers, I won't attack.
- When Alice attacks, I'll cast Bladebrand, and then attempt to block with Charming Prince. This makes my decision not to attack "make sense".
- Obviously Alice is now going to tell me that I can't block, and I'll say, "Oops". If she doesn't tell me I can't block, I'll still point it out myself before damage to not intentionally make an illegal play.
- She'll think I must have made a mistake and am not holding Gideon's Reproach, because if I were holding Reproach why wouldn't I attack? I gain nothing and miss out on two damage in this case.
- So she'll go for the win with Giant Growth and then I blow her out with my Gideon's Reproach.
Is this play permissible?
Aside: Alice wins anyway if she casts Giant Growth before attackers, but for the purpose of this question, ignore this potential line of play.