Gajeel devoured shadows, Natsu devoured lightning, which they now are using like it's theirs without these side effects you talk about. Neither of those skills are particularly related to one another. The point is that them only being able to eat specifically their own element, is not true. That doesn't mean they suddenly can start eating everything they want, something I neither said nor implied, but it does show that their ability to eat stuff is broader than just their element.
I probably should elaborate what I was talking about more, because it seems to confuse you. While they were able to eat it, some of side effects were showed at least earlier in the series (Natsu trying to eat Laxus' lightning, and if I remember correctly he had problem after he ate Lacrima). We don't know did Gajeel tried eating other element before (it's possible that he tried and also had side effectes).
If anything this would further my argument here. Since Gray should have side effects at the first.
So that Gray somehow absorbed MG curse, despite it not being ice related, is within the realm of possibilities.
Yeah, I was affraid that it will come to this, I was thinking to edit a comment, but okay I will elaborate now. Natsu can eat
Fire,
Dragon Slayer Magic. Also when I referred to Gray's ice in last post I was referring to his Ice Make magic and not Devil Slayer Magic.
I will try to rewrite Gray's case from last post:
If there is similar case with Gray, than he would be able to eat Ice (any type, except for his own Devil Slayer Ice), and other types of Devil Slayer magic, he would be also able to eat Ice coming from Demon (like Atlas' magic, Natsu consumed), but he wouldn't be able to eat Memento Mori, since it wasn't Ice's magic.
Like I said MM is not Ice and it's not Slayer Magic, either
Adding to that Gray just blasted an attack right through MG, so whether he now became stronger or not is very debatable.
Every time Natsu or other slayer ate other magic, they got stronger the same moment. Gray first fell down and barely was able to stand up.
So that ultimate argument is very brittle, even more so when you take into consideration that I used Acnologia's case as an example. We know barely anything about how he was before he became a dragon, but I doubt he was as he is now. So there is nothing we know about the process of transforming from a dragon slayer to a dragon.
As long as I remember he became Dragon because he took a bath in Dragon's blood. (A lot of baths)
Even if that's not true it still likely was long process, Gray got Slayer Magic just 1 hour ago.
So if Gray reached a stage of demonification that Natsu so far never reached during the process of becoming a dragon, well then you can't say for sure that it means he becomes stronger in that phase. For instance it's in theory possible that you become weaker during that phase as your try to fight the process of transforming, which is probably not just a physical, but also a mental transformation.
While I agree with about mental change and fighting against transforamtion. I still can't see how will Gray become Demon that fast.
Just re reading a chapter, and Mard implied that Gray blocked magic instead of eating it, which mean he become demon before MM hit them. Demons being immune to MM? Possible, but I really doubt that.
Lastly you contradict yourself. First you are talking about how absorbing magic that isn't inherent to an element, causes side effects. Then you say that as the ultimate argument that you are supposed to become stronger when absorbing something. Well then you can easily say that Gray absorbed the curse magic as he is a demon slayer and thus connected, but that it didn't had the power up effect because it's not his element.
I explained that "contradiction" above.
And is there a particular reason you find it necessary to bold my name?
It bothers you? First time see someone being bothered by it. Just my way to show respect to other members, tho, sorry Caliburn.