In contrast to conventional wisdom, certain materials become more plastic at low temperatures. High entropy alloys (HEAs) are a case in point; the ductility of HEAs increases when the temperature is lowered.  We have been using neutron diffraction to study this unusual deformation behavior.  In situ neutron diffraction measurements at 15 K in CrCoNi-based HEAs revealed a myriad of deformation mechanisms, including stacking fault, twinning, phase transformation, and serration, in addition to dislocation slip. The in situ neutron diffraction data were used to estimate the contributions of different deformation modes to the strain hardening.  It is shown that the cooperation of different deformation mechanisms led to the extremely large ductility at low temperatures. The increase in ductility at low temperatures has been observed in other alloys as well, including Mg and refractory high entropy alloys.  These new data call for a revisit of the deformation map at low temperatures.