If you feel like you have high BP compared to others and lack ninjas, then go for event ninjas. They can beat someone with 10k-20k more BP if have right formation and high initiative. If you have ninja and lack BP and dont know to spend coupon then buy charm materials. After that buy all initiatives clothing.

If you have low BP and few ninjas, then i suggest getting at least two event ninjas ofcourse not neglecting initiatives. Power with 90k vs power with 80k has no difference. if the power 80k has higher initiative and better ninja than the 90k then 70% you win all the time.

I am level 91 with power of 84k and use kisame fusion and edo deidara, recently beat 100k power in SWB(which is rare) and i got around 7600 initiatives in Pos1. My Pos1 always attack first than his Pos1. Deidara scaling is scary, round 2 deidara mystery, I literally damages 60% hp of all his ninjas plus ignite them. By the end of round 2, 2 ninja die and the remaining at the death door.

The point here is that if you have better ninja and better initiative, if your not dumb, then 70% you win all the time.