This page shows in what ways Grux is weak against Feng Mao. Or in other words what actions should Grux do to receive minimal damage from Feng Mao. Note: any hero isn't always strong or weak against another one. It depends on many different factors so please keep that in mind while adding your tip.
This isnt very helpful, also by grux I think you mean rampage.
Try to avoid all of gruxes rock throws as feng mao then when the time is right and his ability's are down melt him with your ability's or ultimate.