I have no idea It really was just an art request I've never played the game before!
Though I have heard some interesting theories about cutie marks occasionally changing when a pony gets older, like the older retired ponies with smoking pipes, coffins, etc. for cutie marks. Doesn't really seem like something you'd think to see on a foal's flank, does it?
One thing you did that i agree strongly with is that the mark of the outsider should be on his flank, like all ponies. Many other artists have drawn ponies with the outsider's mark on the forhoof, which to me seems lazy and illogical.
Honestly, I can see both sides (even though I've never played the game, nor do I know the plot very well.) It could make sense to put the Mark on his forehoof since he recieved it as a full-fledged adult and probably would have had a different mark already on his flank by then. (I've seen a crow mark, for example) I can't recall if one can change their cutie mark, and if you can't, then it would make sense to put it on the hoof (also for game-accuracy) However, if you can change it, then I do think it would go on the flank since it's a display of ones unique ability. Not to mention, I simply like it better there
Before I begin, let me just say that I really do like this picture.
BUT I kind of disagree with the Mark of the Outsider being Corvo's "Cutie Mark". Cutie Marks are supposed to be symbolize what makes you unique, or a major personality trait. And Corvo is not the only one touched by the Outsider, and it was only very recently that The Outsider came to him. A better symbol would be the Flag of Dunwall to show that he is loyal to the crown... of course they don't really show such a symbol in the game so The Outsider's mark is the best we've got.
A very fair point! Better than one I could have come up with myself! (Especially since I've never played this game before, and it was requested by a gal who has ALSO never played this game before, for her boyfriend who loves both Ponies, and this game.) The pony half of this picture is all that I'm really familiar with