Not sure if it would be game-breaking; 'Q' on Nocturne
Not sure if this belongs in this section, but skins and champion concepts seemed all about skins and aesthetics. Anyway, I had this idea about Nocturne that I thought would be cool but not sure how others feel about it so I'll ask. Would it be too much to have Nocturne's 'Q' allow him to go through walls? Now before you say 'no' I believe it would be another tool in his kit that is lacking (imo) at the moment because of the reduction in range on his ultimate. This would only happen when he is on the a Dusk Trail, if you are caught just in the middle of a wall you pop out on either side or take damage or something.
There are plenty of other champions with dash or teleport abilities that allow them to jump over walls and escape. (ie:http://forums.na.leagueoflegends.com/board/showthread.php?t=3341169) (Also, the new Rek'Sai) The class on Nocturne is assassin but how can you chase down opponents if they have such easy escapes? You can ult in and put yourself in the middle of the fight but leave you with no way to chase the more elusive champs? The only CC he has is if he can stay in range. Other champs with ability based escapes will be almost impossible to catch if you're Nocturne. This would allow you to chase down those champs who flash or dash over walls. Also, this would be a decent escape ability if you are ever caught in a bad spot to get away. Also, this would allow more map mobility for when the ultimate is on it's super long cooldown, and gives you the option of coming at people sideways when your ult is down.
In my opinion, it is also lore friendly. Nocturne is supposed to be some ethereal creature from nightmares. You will fear him when you see his duskbringer coming from over a wall where you didn't think to look, or just when you think you've gotten away. You will finally start to be paranoid that he could be coming at you from anywhere at any time. :)
Edit: well got some discussion which I hadn't thought of which is enlightening. Overall it seems people are saying something could be done with duskbringer, whether it is this or something else remains unclear though.