Is it permissible to intentionally make an illegal move in order to bluff?

Question

Imagine this situation -

Alice's board: a tapped Steel Leaf Champion, Ghor-Clan Rampager in hand (which Bob knows about because of an earlier discard spell)

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:

1. Although Alice has no blockers, I won't attack.
2. When Alice attacks, I'll cast Bladebrand, and then attempt to block with Charming Prince. This makes my decision not to attack "make sense".
3. 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.
4. 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.
5. So she'll go for the win with Ghor-Clan Rampager and then I blow her out with my Gideon's Reproach.

Is this play permissible?

Answer 1

No, you are not allowed to do this because doing so would be a violation of tournament rules at every level.

At Competitive and Professional REL, the Infraction Procedure Guide determines how judges handle rules violations. The action described in the question is a Game Rule Violation, a sort of catch-all category that includes making invalid attack or block declarations. In addition, this action is dangerously close to Cheating as defined there:

A person breaks a rule defined by the tournament documents, lies to a Tournament Official, or notices an offense committed in their (or a teammate’s) match and does not call attention to it.

Additionally, the offense must meet the following criteria for it to be considered Cheating:

• The player must be attempting to gain advantage from their action.
• The player must be aware that they are doing something illegal.

The action described involves knowingly breaking a game rule for the purpose of gaining an advantage.

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At Regular REL, the Judging at Regular REL document reigns. In that document, the "Serious Problems" section lists the following:

Knowingly breaking or letting an opponent break game or tournament rules, or lying, in order to gain an advantage. “Bluffing” about cards opponents can’t normally see is permitted.

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If Bob instead tries to declare the block and then takes it back all within a single action, it's no longer reasonable to interpret it as an illegal action. Instead, he's just thinking out loud through the applicable requirements and restrictions that determine blocking legality. So the rest of the wouldn't apply and it should be fine for Bob to do that.