Wargames
One Of The Last Real Ones To Do It
With time he will be able to use Gear 4 consistently much like he is now able to handle Gear 2 and Gear 3 without consequences. Awakening is obviously going to be the real gamebreaker since that shyt had Doflamingo turning his entire surroundings into string. I'm not sure how turning his surroundings into rubber will benefit Luffy in combat more than giving him additional momentum but it's clear he will gain it at some point.
I could see him doing some sort of bouncing attack or maybe have a bunch of fist pop up (like gatling gun) and attack the bad guy