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Per WizzLe’s news article from early February:
BHM Chemistry
After you've earned the Hero version of all 5 Black History Month Players, insert them into your lineup to receive the following boosts to all BHM Players in your lineup:
- +1 STR, +1 AGI, +1 SPD, +1 JMP, +1 SPM, +1 JKM, +1 PMV, +1 FMV, +1 BSH, +1 INJ, +1 STA, +1 POW
Hope that helps. They all need to be fully powered up through their objectives for the chems to kick in.