See Resounding Barrier and Resounding Truth.

Oh! That's a nice use of the four card limit.

Oh! That's a nice use of the four card limit.

Thanks, Vitenka.

That is a nifty mechanic. The big downside is cards like Mnemonic Wall, Snapcaster Mage, and so on can mean this isn't as easy to track as it looks. (Putting it on a Panoptic Mirror is kinda funny but not really broken.)

As an alternative (which also has problems, just different ones): "If you have three other cards in your graveyard named ~,..."

I figure it will be hard to track no matter how it's implemented. Snapcaster and friends do throw a wrench in the works. I'm not even sure that non-planeswalkers making emblems is a good idea.

How about keeping an exiled copy (or even an echantment) around; which once it has enough counters has the effect?

Or exile this on resolution, and either count the exiled copies, or count "forth time you've cast from your hand"? (I think it would be ok to get the emblem by casting copies, but it would be better to avoid memory issues if possible.)

I feel like there wouldn't actually be that many memory issues with this, but maybe I'm mistaken. After all, it specifically calls out on the card that you want to remember if it has been cast. It's not like it's asking if you've cast a different spell four times in the game. Hopefully people would just keep a tally as they cast it.
That aside, I made this because it popped into my head, but I'm thinking emblems should be something kept unique to planeswalkers. After all, Praetor's Counsel didn't use an emblem (thought it was admittedly an easy-to-remember effect).

Likewise they haven't errataed Stigma Lasher to use an emblem, and the stated reason is because they want to keep emblems unique to planeswalkers for the moment.

since emblems work from command zone anyway, i thought of this:

"Do XXX. Then put this card into your command zone.
­: Some activated ability. Activate this ability only if you have N cards named CARDNAME in your command zone."

That would certainly work, though I'm not sure the command zone should be referenced outside of Commander products (personally I didn't enjoys the direct references in this years commander product). I wonder how many players even realize that the command done exists when your not playing Commander.