It's safe to say that Samurai stopped using his fire magic after seeing the imposing vines in his way. It's just not needed at the moment. After freeing a few trapped ponies and racers, Samurai takes a moment to see who has caught up. In doing do, he sees the various powers @Nitobit Moonlight is exhibiting, the moonerang that @Shiny Silvermoon Shiny got, and the increased horn size that @Iridescent Edge Iridescent got.
"Hmm... Well, maybe one fruit couldn't hurt. Please be helpful." Samurai hesitantly eats one of the berries he has been saving. His jacket suddenly becomes a protective cloak, and in his hooves is a pole weapon. On one end, a jumonji yari; on the other end, a naginata. "...You know, I never though about combining these kinds of weapons before. But lets give it a chance!"
With a warrior's focus, Samurai stands up right, concentrates, and prepares his weapon. When the moment is right, he lunges forward and expertly begins to swing his weapon around in many directions. Hundreds of slashes! Tons of vines go down. Somehow, not a single trapped racer gets struck in any way, completely avoiding getting hurt. And the more Samurai keeps this up, the more he creates a tunnel through all these wild vines!
...But he also stops knocking down leaves to do this...