Using Medic Nin (+ my strategy for the Kyuubi Invasion)
Medic nins mean life or death in any battle. I just started playing this game and this is what I learned so far using Sakura and Kabuto and seeing Tsunade and Karin in action:
Two star Sakura's regenerative healing jutsu saves my life, but constant healing (like Sakura, Kabuto, Tsunade, and Karin) is just as helpful. Your ninja with the lowest life left receives this twice per round with two star Sakura. (With Jigokudo Pain, it's the lowest two.)
Use healing jutsu wisely. Putting the battle on Auto sometimes makes you waste a healing jutsu in the very beginning so you can't use it when it matters. Pay attention to your battles and use the jutsu when you really need it. (That aspect of Auto is something you can take advantage of in Survival Trial or Arena matches.)
Make sure your medic can actively fight. Sakura's taijutsu does more damage than my two star curse seal Sasuke sometimes. Kabuto's clones have also helped. Meanwhile, I've been beaten by an otherwise running-on-empty Karin by her poison cloud, and Tsunade needs no comment. (Yikes.) Another thing to keep in mind is combos - Sakura has great combos with my team (Scarlet Blaze, Zabuza, and Sasuke). Check combos by clicking "Display Matches" under the Ninja tab.
Don't forget to level up your medic. Sakura takes priority over my three star Zabuza and my own character, meaning I cultivate, feed, and awaken her before anyone else. I also give her the best equipment and defense, life, and ninjutsu magatama so that she can withstand attacks. I treat her like royalty so she can save me when I'm fighting a tough opponent.
Keep your medic away from types of ninja that have an advantage. Sakura is a water type so I don't place her across from earth types. (Remember that lightning beats earth, earth beats water, water beats fire, fire beats wind, wind beats lightning. Of course, none of that matters in a one star versus five star battle.)
If you don't have a decent medic nin, stall your opponent by putting someone with strong clones like Zabuza, Naruto, two star Shino, or Kankuro (his puppet is like a clone) in front so that the clone protects the actual ninja. I always have two layers of strong nin in front of my medic Sakura. Kabuto has his own clones. You could also use someone with a protective jutsu like Kurenai, someone who resurrects like Orochimaru or Hidan, or just a chakra tank or filler (when I'm desperate in a Survival Trial, I'll throw Hinata and Neji in front so that some taijutsu is blocked.).
Playing smart makes you win more often and makes the game more fun!
About me:
Character: Scarlet Blaze (lvl 37)
Main team: Sakura, Sasuke, Zabuza
Secondary Team 1: Sakura, Temari, Kankuro
Secondary Team 2: Kabuto, Shino, Hinata
Defense Team: Sakura, Kankuro, Naruto (sometimes Kiba)
Offensive Team: Sasuke, Kankuro, Temari (I use this in the Nine Tails Invasion. Kankuro's puppet is the first move and first row, so Kyuubi's first move hits the puppet only. Temari and Kankuro are the second row; Sasuke and I are third because we do the most ninjutsu damage the fastest. If Zabuza had a better offense than the mist jutsu I'd use him.)
With power comes responsibility. Don't copy me completely, please. And I don't know everything about this game yet, nor do I have lots of great ninja, so do your own thing if you think it works.
Thanks for reading!