This is the team I use. It's not entirely f2p friendly thanks to Angel. My Gaara is 4* and has SB +1 for his shield. The buff that Asuma provides and the buff that Gaaras' sand hell provides is amazing for sustained dps. I ended up taking down 24% of ninetails life and got 1st place in damage. If I remember correctly I did roughly 10M damage to the world boss and was able to survive for all 10 rounds.