So far I have been using:
-Main-2 star-Water Dragon Jutsu/ Super Water Shark Bomb
I place my main character in the middle she's quite tanky the way I made her.
-Haku-2 Star
I place Haku in the first square, top row, or the very bottom row next to the main character.
-Karin-3 star
First row behind Haku.
-Kakashi-3 star
Last row, next to the main character OR where I normally place Haku to protect my main.
The way it works is you get to either poison or increase your evasion on Haku/Water Ninja's attack stats first turn... During turn two you c*e Kakashi's Jutsu or the Main Character's Jutsu and do a very long combo using all characters, and it ends with Karin's poison spray. This Burns, Paralyzes, and poisons for the full combo, getting rid of most threats then and there.
Alternativly you can replace Karin with Kabuto or Shippuden Sakura, and Kakashi with Anko or Lee, so one hits knockdowned enemies into a high float to combo with.