We achieve unprecedented nonlinear optical amplification in gas. The gain is 20 times larger than any reported nonlinear gain in gas-filled HC-PCF and 6 times larger than the largest nonlinear gain in standard silica single-mode fiber (SMF). Furthermore, our system can work at any wavelength from ultraviolet to mid-infrared thanks to the nature of backward stimulated Brillouin scattering used in this work. This massive gain enables us to realize a single-pass gas Brillouin laser with 140 mW threshold power. In addition, the temperature sensitivity of the normalized Brillouin frequency shift is found to be more than 30 times higher than for SMF. This platform then opens new avenues in gas Brillouin lasing and high performance distributed fiber sensing.