Solution generator: https://github.com/Jinmo/ctfs/blob/master/csaw16/ivninja/ivninja.py
It was IV calculator, and I tried some IV calculators online.
The binary's check logic was using some formula with some input, and validates the floor-ed integer with CP and HP.
Formula: https://pokeassistant.com/main/ivcalculator?locale=en#ivinstructions
Some are OCR-ed, so I printed some text to it.
I slightly modified HP bar.

Original writeup (https://github.com/Jinmo/ctfs/tree/master/csaw16/ivninja).