GB ability is Wanos Hope for the Wastelands and such.
The poisoned Rivers where Tama drank from in the beginning of wano.
I would not be surprised if GB has the ability with his plants to clear and filter the water,and get rid of the poison .
Its now pretty clear his introduction in wano was planned from the beginning due to his powers.
How his confrontation with the Alliance will Play out

I mean i got pre timeskip sabaodyvibes not in a sense they will lose to GB now ,Luffy will not be decleared a yonko only to lose his next fight .
Wano is still in Act 3 and an Admiral shows up .
I think Act 3 Ending will be as impactfull as Sabaody back then .