de z ▁saved ▁from ▁a ▁supply ▁clos et ▁and ▁pre fers ▁to ▁be ▁pol ished ▁by ▁Lem on ▁P ledge ▁instead ▁of ▁W index . ▁He ▁ass ists ▁Leo ▁Val de z ▁in ▁construct ing ▁the ▁Ar go ▁II ▁in ▁B unker ▁ 9 . ▁Event ually , ▁Leo ▁programs ▁a ▁talking ▁mini - h olog ram ▁of ▁G le es on ▁H edge ▁onto ▁B uf ord . ▁ ▁Car th agin ian ▁Ser pent ▁- ▁A ▁ 1 2 0 ▁ft . ▁ser pent . ▁In ▁The ▁Dark ▁Prop he cy , ▁Apol lo , ▁Meg , ▁and ▁Leo ▁face ▁this ▁mon ster ▁while ▁making ▁their ▁way ▁to ▁Com mod us ' ▁la ir . ▁Apol lo ▁trick ed ▁it ▁into ▁crash ing ▁into ▁a ▁nearby ▁condem ned ▁cond imin ium . ▁ ▁Cent ic ore ▁– ▁Dead ly ▁ant el ope - like ▁cre atures ▁who ▁were ▁task ed ▁to ▁guard ▁the ▁C ave ▁of ▁Tro phon ius . ▁Due ▁to ▁their ▁end anger ed ▁status , ▁Apol lo ▁goes ▁to ▁great ▁lengths ▁not ▁to ▁kill ▁them ▁as ▁he ▁so aks ▁himself ▁in ▁the ▁waters ▁of ▁Let he ▁and ▁M nem os y ne . ▁ ▁Cer ber us ▁– ▁The ▁three - head ed ▁dog ▁who ▁gu ards ▁the ▁entrance ▁to ▁the ▁Under world . ▁In ▁The ▁Light ning ▁Th ief , ▁he ▁be fri ends ▁An nab eth . ▁He ▁also ▁appears ▁in ▁The ▁Last ▁Olymp ian ▁when ▁he ▁is ▁playing ▁with ▁Mrs . ▁O ' Le ary