Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Threats to Janna with this build
So im a only a silver support main, ****py, right? Anyway, I've found this build works the best for me and I would like to know what you think about it.
Janna is best during a teamfight. You need to figure out when and where the fight is going to take place as well as where the carry is going to be at that time. With that info you then need to figure if anyone is going to charge the carry.
If so then charge up your Q to that exact point. Wherever that may be. It can stop a dash as well as knock them up long enough for the carry to get away after they have blown their gap closer.
If you believe your carry is going to be safe then you need to save it until it's needed while being chased or chasing.
As for your W, just use it to lock down left overs after, or during the fight.
Your E should be used on either the main damage absorber, or the carry depending on who is going to need it. The carry if they are going to be focused, and the tank for them to buff their health even more.
The R should mainly be used when your carry is jumped on and you have used Q, or don't have time to cast it. Another reason is to heal your team from the outskirts of the fight.
The other thing you need to take into account is your Locket. When should it be used? Use it when either the enemy team first engages, or once your team engages.