Self-expansion without regard for others’ well-being may represent the dark side of an otherwise healthy motive. Guided by Amoebic Self-Theory (AST), we developed the Engulfing Self Scale (ESS) to measure acquisitive tendencies across AST’s three domains of the self. Four studies revealed that bodily engulfment appeared generally benign, and that the problematic aspects of social engulfment were generally restricted to interpersonal contexts. Spatial-symbolic engulfment motivation was linked to a breadth of problematic indices such as psychopathy, Machiavellianism, narcissism, psychological entitlement, social dominance orientation, economic system justification, greed, and valuation of power. It also predicted reluctance to expose a cheating group leader when doing so would threaten one’s own positive outcomes, greater justification of a looter’s behavior when prompted take his or her perspective, and greater justification of self-serving reward allocations after defeating an ostensible competitor. Spatial-symbolic engulfment may be a motivational fountainhead for behaviors that negate others’ well-being.