Swamped

He's waving around a bottle. It looks to be open. But why in the world...

The first answer that pops into your head is "because alcohol is highly flammable", and it looks like the mystery man has the same idea. He lights a match and a plume of flame pops out of the bottle before he flings it at the oncoming mob.

It hits the ground, and the flames start popping up. Must have poured some out beforehand. It effectively creates a wall, with only a handful of gangsters on this side of it. There are narrow gaps on either edge of the street, probably to keep it from spreading to buildings, but the hostel guards soon take position at the gaps. The few who dare cross are soon dealt with.

"Grab some water and douse them, you fools!" someone calls out from the other side of the flames. Might be Heron. But it'll be too late by the time they carry that out - the handful on this side are already half down, and they can't get effective reinforcements.

On top of that, it looks like the stranger has another trick up his sleeve.