Xiphophorus nezahualcoyotl Rauchenberger, Kallman & Morizot, 1990 is a northern swordtail whose biological significance is best understood within the broader evolutionary, behavioral, and genomic research framework of the genus Xiphophorus. This mini-review synthesizes current knowledge on the species’ taxonomy, phylogenetic placement, distribution, ecology, reproductive biology, sexual selection, and relevance to comparative research. Particular attention is given to the size-dependent alternative mating tactics of males, including the continuum from coaxing to coercive behaviors, as well as the occurrence of false brood spots and female-like pigmentation patterns that provide a distinctive example of female mimicry and sexual deception. Recent phylogenomic evidence further places X. nezahualcoyotl within the reticulate evolutionary history of northern swordtails, including documented gene flow with X. continens. The review also distinguishes the species-specific evidence from the broader biomedical significance of the genus, particularly the classical Xiphophorus melanoma models based on other species and interspecific hybrids. Although X. nezahualcoyotl is not a principal biomedical model, its combination of alternative reproductive tactics, sexually selected traits, polymorphic female mimicry, and introgressive evolutionary history makes it a valuable comparative system for studying sexual selection, behavioral evolution, hybridization, and speciation. Important gaps remain in species-specific knowledge of life-history schedules, population demography, physiology, and detailed reproductive parameters, highlighting opportunities for future research.