­Malentis Privateer + Astral Arena

Ok the arena is "One fight at a time please, no pushing gentlemen"

And. Hmm, a vanilla. 2/2 pirate. Well, that's a bear then, isn't it? And "Pirate Bear" is already in my dropdown; so I wonder where I already created that? Oh! Hah! ­Tetraid Ursine which is already a card which plays with blocking expectations.

Ok, blue gets evasion. Red gets "Hah! Stop me puny mortal!" LEt's do that. Red gets 2/2 at cmc2 with a downside, or 3 with an upside; and the upside is nice and simple and useful for red. No flavourtext; leave the terrible pun in the name alone; more impact there.

Searching for "Pirate bears" by the way.. leads to a serious level of wtf. http://naughtybear.wikia.com/wiki/Pirates

Oh, simple but effective, I like it. You could embrace the flavour further with "must be blocked by exactly one creature if able"[1], although it's not likely to make much difference.

[1] Although come to think of it, if it says "by exactly one", and someone has two "can't attack or block alone", do they get to choose between blocking with 0 and blocking with 2?

I have no idea; and so will say this simpler version prevents such brain pain.

"If you Wear the Master Naughty Costume... the Pirate Bears will attack you on sight regardless if they know your Naughty Bear or no."

Fair enough.

Jack - I... don't know. I was about to post the below, but I realised I'd stopped making sense. You may indeed get the 0-or-2 choice, although my gut feel (often wrong in Magic rules!) says you should only get the 0 choice.

Jack - that falls under the heading of restrictions and requirements. When you attack or block, you must fulfill as many requirements as possible having violated as few restrictions as possible.

So here "can't attack or block alone" is a restriction, and "must be blocked by exactly one" is (I think) both a requirement and a restriction. You can't honour both restrictions, but ...

I'd interpret "must be blocked by exactly one creature if able" as a requirement, but not a restriction. (It includes "if able" which seems to make it unlikely to be a restriction.) So if a creature with "must be blocked by exactly one creature if able" is attacking, and the defender has two Ember Beast, then the attacker's requirement for 1 can't be met, so defender gets to choose 2 or 0.

Confusingly, the situation isn't quite the same with Krosan Vorine. That has a separate requirement (Provoke) and restriction (no more than one), and restrictions trump requirements, so defender isn't able to block with the targeted Ember Beast either on its own or in conjunction with another Ember Beast. (They would be able to block with some random other vanilla though.)

On colour distribution, "you must block me" is normally green, but red and white get to dabble in it from time to time.

Oh, good analysis, thank you. I don't know exactly how my putative ability would be phrased, I added "if able" automatically, I'm not sure if it should have it or not.

I agree that it feels like it should default to zero, but there's no clear implementation of the rules that makes that happen without rewriting it to be two different effects.

I think part of the confusion is that I'm not sure if "restriction" and "requirement" refer to negative and positive instructions ("can't attack" or "must attack") or to "must" and "if able" instructions, or if it's assumed, but not stated, that those always match up.

So I think I instinctively interpret "exactly one" as both a restriction "at most one" and a requirement "at least one". Then if you attack, all the restrictions are met by not blocking with the ember beasts, and then you're unable to fulfil the requirement. But I'm not sure there's any way to legally support that interpretation. (I do think "choose 0 or 2" is likely to be misunderstood even by non-pedants.)

"Restriction" and "requirement" in 509.1 terms are basically negative and positive statements, yes. "Must" is a positive requirement; "can't" is a negative restriction. I think Wizards probably use "if able" as a clue in templating towards the way that restrictions trump requirements.

Thank you, that makes sense.