<p>Ludic design in mental chronometry seeks to enhance engagement through socio-interactive elements. The present study examined whether a co-actor duel context influences both performance and subjective experience. Participants completed speeded arithmetic at two difficulty levels (easy, hard) under two context conditions (alone, duel) in a mixed within-subject design. Self-reports of engagement, distress, and worry were obtained before and after tasks. In the duel context, participants completed problems more quickly, accompanied by a small rise in errors, which however, remained far below the 10% margin allowed by duel rules, indicating that the increase was not a deliberate sacrifice of accuracy for speed. We interpret the speed-up as improved efficiency with preserved engagement, where the modest error rise reflects the probabilistic cost of reduced checking time rather than relaxed accuracy criteria. Such minor differences are unlikely to be consciously detected and therefore are not introspectable as a performance decline.</p>