This short review paper examines the uniqueness of metastable high entropy alloys (HEAs) that transform during plastic deformation. The linkages among alloy design induced metastablilty, processing induced “high enthalpy states” and evolving deformation micromechanisms are intriguing. One key aspect is the adaptive nature of deformation mechanisms because of activation of different micromechanisms during plasticity. This activation of deformation micromechanisms is attributed to transformation-induced plasticity in γ-f.c.c. phase and the evolving nature of c/a ratio in the ε-h.c.p. phase during deformation. As a result, metastable HEAs have good strength-ductility synergy and exceptional fatigue strength. © 2021, The Minerals, Metals & Materials Society and ASM International.