Probably shouldn't be printed, but another idea of how to make "all-in" matter in red :)

Can it have a less silly name? :)

Yeah, feel free to change it :)

Oh, no. I like this guy. Obviously the ability already appears in Magic on the card Masako the Humorless, which leads me to believe that this card isn't really red, since the ability feels more like vigilance. Actually, what if we made this card white, and left it as a sleeper card that secretly worked with all in? It seems to have the strangeness that our mono-white creatures carry...

As for the way it's worded, I think we need two sentences. Just because it can only block if it is tapped, doesn't mean that it can block if it is tapped. That's like having a non-flying creature have the text "This creature can only block flying creatures". It doesn't really do anything.

I think "being able to block despite X" is white, but "able to do X if you attacked" is red, so I think this version could be either (which is why I thought it was funny). I agree with your logic, but I'm not sure it really fits in white: if it has the "block only if" it doesn't feel very white (since when can white not block normally?) and if it has has "can block if", then it doesn't especially aid the red theme more than any other tap effect.

I agree the flavour works, but I don't know how much cross-color synergy we want to look for. So, um, I guess I don't know, either way would be fine with me :)

Can block iff it is tapped?

Yes, I suppose that would be the simple white solution. Red, though, really would need "~ cannot block creatures if it is untapped, and can block creatures if it is tapped."

I think "can block only if tapped" would mean "can't block at all" to a logician, but imply "can block if tapped, but only then" to a normal person -- I'm not sure which usage magic follows (I'm trying to think of any examples. I agree they probably want to spell it out, but wish it needn't be that clunky).

I repeat: "If and only if"

The only one I can think of, which tends to lean toward me is Chaosphere, but I admit, it's a poor example.

V: "if and only if" is what I'd say and expect it to be unambiguous, but I'm not sure whether or not it would be clear to normal people :)

DrJones's set Orobis has a fantastic keyword mechanic "sidewalk" which has reminder text as follows:

> Sidewalk (This creature can attack tapped or untapped. While this card is tapped, it can be blocked by and only by tapped creatures.)

So he thought "by and only by" would do.

ROFL. Sidewalk is awesome, I wish I'd seen it before :)