For Challenge # 074, and making sure that Pirate World doesn't devolve into 'Ship World'. ;)

My reasoning behind making Mark is that a good pirate set should be filled with cursed artifacts. But most people don't want to play artifacts with negative effects in their deck. One of the nice things about Pirate World, however, is that it's bound to have a fair amount of permanent stealing, because... Pirates. Unless the set mechanics get in the way, I assume, at the very least, that Steal Artifact would be reprinted in this set.

So Mark is an attempt to get sneaky, and put a few curses on your own artifacts, watch your opponent steal them, then laugh in glee as you reveal that your mark was really a curse. It's the ideal scenario, though there's enough interactions going on with this card, that it should still be fun without the perfect setup.

I don't understand this at all. Also, Mark doesn't work because all face-down permanents are creatures.

That's easy to hand-wave away. If a face down permanent is attached to another permanent, then it must be an Enchantment - Aura with mark. You could even mix morph and mark in the same set without too much confusion (though I wouldn't), since you'd be able to tell which was which based on card orientation - just as long as people don't stack their morphers ontop of each other (which they shouldn't be doing anyway).

Outside of that, what don't you understand Link? The idea doesn't seem that different than morph... I'm not sure where the problem could be.