This line up works for solo difficult mode for me at 50k power with about 3300 points. I hope it helps people that have these ninjas :)
First round, just let Sakura and auto attacks/combos kill them.

Second round, focus Mabui first with shark bomb followed by Mei's mystery next turn.

Third round, focus the non-clone Darui and use all mysteries, try to heal at the end.

Forth round, focus Raikage-he will probably kill someone first round just try to focus him down, Mei will control Onki if he survives the auto attacks.
your mysteries from mei and WM should bring the Raikage down and Bee will go down next round.