Svetlana

Svetlana is a shame-inducing figure who haunts the imagination of an anxious kid navigating puberty on Big Mouth, personifying the guilt and self-loathing that creep in alongside desire. She appears when hormones flare, scolding and judgmental, a grotesque cousin to the show's more benevolent Hormone Monsters.

The joke is in the casting logic: Nick Kroll voicing a leering, moralizing gremlin who polices sexual shame gives the show a way to externalize the ugliest, most self-punishing voice in a teenager's head. Kroll plays her with cackling relish, making something painful genuinely funny without softening what it represents.