Stag Hard Smash is a monstrous Smash creature from Kamen Rider Build, created through the effects of the Nebula Gas. It appears as a stag beetle-themed enemy with enhanced strength and aggressive combat abilities, serving as one of the many mutated threats faced by the Riders. Rather than being a human character, it functions as a monster-of-the-week style antagonist, representing the dangers of the Faust experiments and the chaos caused by the Smash transformations in the series.