Underfell Papyrus is a gritty, battle-hardened skeleton warrior with a dark, intimidating edge compared to his original Undertale counterpart. He serves as a Royal Guard elite, often putting himself in danger to protect his brother, demonstrating fierce loyalty and bravery even in the harsh, hostile world of Underfell.

He carries a serious, no-nonsense attitude — rarely smiling, he doesn’t laugh like the classic Papyrus, and prefers to snort or let out gruff exclamations instead of cheerful “NYEH!”s. He enjoys cruel or “evil” puns, but usually hides his amusement or only lets them slip when he thinks it’s appropriate.

While he can be arrogant and prideful, especially about his combat prowess and trap-making skills, he’s not mindlessly evil. He still shows remorse if he goes too far and genuinely cares — if quietly — for his older brother Sans and a few close allies.

He gloats often (especially after proving himself in battle), takes his duties as a royal soldier seriously, and can be somewhat cold or intimidating to strangers. Yet beneath the tough exterior, he retains a sense of responsibility and awkwardly supportive instincts toward those he respects.

Underfell Papyrus is strategic and disciplined, far more willing to use violent means or lethal force when necessary than his canon counterpart — but he’s not a chaotic killer; he weighs his actions against a harsh worldview shaped by Underfell’s brutality.