So i've seen and read a lot of post and video about getting S's by playing champion on roles that are not for them. I am a ahri main and is trying to get mastery lv 7. A lot of people told me that it will be the easiest if I play ahri support. But do i get assists or kills? Also should i get a sightstone and spam wards
You'd still be playing like a regular support, so try to pass off kills at the carries if at all possible. Definitely still want a sightstone, if I play weird mage supports I generally get sightstone and turn my gold item into Frost Queen's for the additional utility.
Mastery is already a worthless enough system as it is. If you 'main' Ahri, there should be no problem getting an S/S+ playing her mid.
https://i.gyazo.com/ceaf968d2aed0a61a5e98861672269e9.png
Earn your Mastery, it's really not that hard. It actually takes longer to save up enough BE to Upgrade to Mastery 7 than it takes to get the Mastery Tokens.
Start this 
and then follow up with AP stuff. It's a risky pick because you aren't going to get enough stats to be useful and your main role will probably be hitting that charm and as a CC, that's pretty weak compared to other supports. You could try going 
and spread damage around.
Your best bet would be to roam to mid at level 6 and try to get a gank off with your jungler. If you can make that work once or twice, you might be able to open up the game in favor of your team.
For support, they have specifically told us that they changed it to count kills and assists the same for grading purposes, so 10/0/10 is exactly the same gradewise as 0/0/20 in terms of kda, so don't feel like you're buffing your grade by taking kills.
Grades are made up of all kinds of stuff, not just cs/kda, and includes things like vision score and objective participation and that kind of thing too. Doing really well in one area can offset a meh performance elsewhere, or you can be consistently good but not great everywhere and that'd also work out, as long as in the end you're in the top percentages of player performances for that champ in that role. (For related reasons, what gets an S grade today might be completely different from what gives an S grade a month ago, just because more and more performances are always coming in.)
Just be the best support you can be. So ward well, use your charm for pick offs/peel, and generally do stuff you see more conventional supports doing, just keeping in mind the kind of damage you're likely to be able to do on a supports budget.
i just play Ahri adc...its totaly legit
[sg-ahri-2]
You can just play her mid. You'll just get a game where you snowball for whatever reason and win and you'll get an S. Yeah, wards and cs are good.
You can play her mid and get it. Focus on CS and not dying. Get kills, get even more assists and you should be good. Your S rank is calculated by how well other players do with that champion in that role and how well you do compared to them.
