Try casting spells now.

What does protection from mana do? Mana can't target anything, be attached to anything, block anything (it isn't an object), damage anything, control anything, or own anything.

(Of course if you don't care what it means, or just make up stuff without regard to it, then that is OK. I sometimes also make up Un-cards whose meaning is deliberately unclear, and this card is silver border, so OK.)

So yes - this is my silly set; and it's silver border. Which means it does things wrong.

As the rules stand? Nothing, except in combination with one very specific card (which brings back the old mana-burn rule). There isn't even a legal sub-type of 'mana' so you can't bring out a creature this would affect. (Again, silver border says you can have anything as a subtype, though.. so this would interact with a few odd cards that let you make up new creature types.)

The obvious intent would be "Players cannot have mana in their mana pool" or something like that. Which is slightly less ridiculously broken now that it used to be (since casting spells then tapping the mana to pay for it became legal).

But yeah - this set doesn't really do rules; it does "I provoke you into wondering a bit".

What's that specific card? It used to be mana burn causes life loss rather than damage, so protection still would not be of use.

Uh... R&D secret lab I think? The un card that says cards work the way they worked when they were printed. You can use that to bring back a card that cares about mana burn to bring the mana burn rule back into play :)

And.. yeah, I didn't know it was life loss not damage. So I guess that wouldn't work. And it wasn't even a rule in the unlimited rule book, so I can't check :)

­R&D's Secret Lair says ignore all card-level errata. It doesn't revert the game rules

­Yurlok explicitly brings back mana burn, but yeah, loss of life not damage