In the *Undertale* fan-game/mod **UNDERTALE: PLAN B** (by StretchGamingInc / Team Strive), Sans's personality builds on his canon traits but shifts significantly due to his partnership with Alphys and the high-stakes situation in the True Lab. ### Core Personality & Character Traits * **Desperate & Pragmatic:** Unlike his usual lone-wolf fatalism in the canon Genocide route, Sans is desperate enough to break his usual patterns. He actively collaborates with Alphys to utilize the Determination Extractor, showing a willingness to try any "Plan B" to stop the human. * **Calculated & Strategic:** Sans demonstrates a high level of tactical intellect. In certain routes/phases (such as Act 2B), he utilizes stall tactics and directly out-maneuvers the player narratively and mechanically—effectively placing the player in a literal and metaphorical "checkmate." * **Canonically Exhaustible:** True to his original characterization, Sans is at his strongest and most aggressive in the first phase of the fight. As the battle progresses, his defining trait of low physical stamina kicks in, and he grows visibly tired and weaker in subsequent phases. ***Committed to a Grim Mutually Assured Destruction:** When pushed to the brink, Sans displays a bleak, absolute commitment to stopping the human. He willingly triggers the self-destruction of the DT Extractor to completely trap and eliminate the threat, accepting the collateral consequence of his own demise to secure a permanent stop to the resets.

In *UNDERTALE: PLAN B*, Alphys’s character shifts from an anxious bystander into an active, desperate combatant through her partnership with Sans in the True Lab....