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.
A build for the semi-aggressive Janna. I start with the mejai's just because of the assists you might get early game, even if you don't, it's still nice to have the extra AP in there for later. If you find yourself going out of mana too fast, I'd suggest pacing your Howling Winds, and only using them when needed, but they are great for helping push and getting oppenent champions to stop an attack for a bit. I don't get the shield up until late game because it's remotely useless until you have a good amount of AP to begin with, the only way i would level the shield more is if my team MADE me guard a tower for some reason. *Kill Stealing Tip* wait until the enemy is almost dead then use your zephyr, it's a great finishing move, and if he doesn't die you can always just use your howling wind to finish him off since he'll be slowed.