To seek optimal strength-ductility balance in metallic alloys, athermic phase transformations upon plastic deformation are regarded as one of the most effective approaches. Decades of efforts in ferrous alloy design have documented the significant role of strain-induced martensitic transformation in mechanical performance improvement (namely, the transformation-induced plasticity effect, TRIP). Provided its mechanical benefit, the resultant transformation product of the TRIP-effect, martensite, is yet destructive. The extensive defect density within the martensitic phase and the hardenability discrepancy with its adjacency can lead to local embrittlement and hence fracture, inevitably rendering an extremum of property improvement. In light of this, the present talk will reveal two potential solutions: a sequential martensitic transformation mechanism and a mechanical faulting response. Further insights into mechanistically-guided alloy design will also be discussed.