Support
I completely understand that ADC right now is not loved by a lot of people. I know that "supports are always blamed". What I don't understand are the people that get filled into support and just don't want to do the role correctly. I don't care who you pick, I really don't.
If you are going to play support protect your ADC EARLY. It's your job EARLY to help your ADC get off the ground and then shift to helping the team the best way possible. That may be by engaging or by shielding and healing. You may just need to use all of your abilities to protect your jungler if they are the most important on your team. You may be playing support brand with enough utility coming from the other lanes so the best way to help your team is nuking them.
Supports in general don't build for stats as much as for utility. Build what will help your team. If you want to roam, hell yes get those mobi boots and zip to the other lanes. If you think that the other team is doing a little too much damage get a locket or a redemption. If your jg Yi and adc Jinx are stomping, build an ardent censor or a knight's vow.
Don't just follow a cookie cutter build. This isn't a carry role that just does damage so build damge. You aren't a full tank role that builds defence to soak damage. You are meant to assist your team as a whole, depending on the situation.