Senna, I think she's the strongest ADC right now. Why? Rageblade + Kraken combo. She can auto attack you to death. It's also easy to play her. She can play passively and aggressively. You need to get used to her delayed auto attacks but it's not that hard. After hitting lvl 6, Senna is really strong in fights. She can use her R to help teammates on the whole map, damage enemies and shield allies. Her Q later in game will deal massive damage and heal a lot, same for R, Senna Late game can go even with champs that were ahead a lot. She has really good synergy with Sion, Naut and Leona, they have a lot of CCs of course. Leona and Naut are good if you want to play aggressively and do a lot of all-in, with Sion you can easily find engage everytime you have minions around and play passively. Runes are pretty good in terms of playing passively/aggressively. Glacial helps you to run away and slow enemies when they want to get away. Minion dematerializer helps you to get first 3 cannons. 3 cannos is something around 270 gold, almost 1 kill. Of course free boots, so you don't need to spend additional 300 gold on them, and ability haste, cause Senna has decent cooldowns but is always good to reduce them. For the secondary tree I've chosen the precision tree. Triumph will help Senna in bigger fights. She'll take a lot of damage because of how paper she is. Triumph will at least heal some of it. Remember she's easy to one-shot, so champs like Zed can just dive onto the back line and one-shot her. Legend: Alaracrity will help in getting better attack speed. AS was always the weak point of Senna. With this you'll stack some Legend stacks and get more and more AS over the course of the game. Keep in mind, try to grab every Sennas soul. Later on, if you'll keep gathering them, Senna can outrange everyone with her 700 auto attack range. She can easily auto attack you through walls and stuff, and even hit tower without getting damaged, with no minions. Well, I hope you'll win a lot with this build. Wish you luck everyone!