User blog comment:IamJakuhoRaikoben/Chapter 411: Quid Pro Quo, Review./@comment-4449950-20141201232911/@comment-7418318-20141203104235

Two counter-points:
 * Memento Mori or Thorn: That's like saying "If Laxus had used Earth Magic instead of Lightning Magic Natsu couldn't have absorbed it." What does it matter for the argument I made whether it's Thorn Curse or Memeonto Mori Curse? They are both Curses, thus equally "edible" within the theory I put out.
 * Slayer need Elements: Considering that we've already seen Poison, Light, Iron and Shadow Slayers that's pretty clearly not the case. If Rogue wasn't there we might see it as "matter or energy", but Rogue fucks even that loose definition up, since Shadows are the absence of light. I think a magic can't get any more "elemental-less" than being the very absence of something else.
 * Lullaby: I think that Lullaby is a bad candidate to judge anything from. For one thing it was created out of a magical or cursed item, so it's most likely different from the Demon Gates and Mard. And for another it was taken down before it could even cast it's main attack. Not to mention that it uses "curse magic"... so it's anyone's guess if it's a magic that's called curse, or a curse that people who didn't know better mistook for being magic.
 * Galuna: Why would you even mention them? They didn't even use any abilities except for transforming into Human shape... which incidentally is an ability similar to what the Demon Gates could do too... but that's not really relevant for the curse vs. magic matter I think.

Since Gray wasn't visible when he did whatever he did, it's impossible to say whether his body first changed and then blocked, or became like that from blocking MM. And Mard Geer himself seemed to have no idea how Gray did it either. He didn't say "you blocked it by...", but rather he asked "is that how you managed to block...?"

You do make some good points for your own theory, but I still wouldn't want to bet money on which one is right. Or we could both be wrong.