The general water team for Nine tail is:
Haku, suigetsu and a 3rd ninja. Guy works really well as that 3rd ninja.
With above team, go rounds like this:
Round 1: Haku barrier
Round 2: Main
Round 3: Suigetsu, Haku
Round 4: Haku, main, Guy
For summon: Use tonton, he has bonus against world boss.
Dont use iruka here. Since iruka only buff konoha ninja, he's wasted on Haku and suigetsu.
For water users, suigetsu is great. His standard/mystery does elemental dmg, attacks twice.