 The episode has received mixed to positive responses from critics . Zack Handlen , writing for The A.V. Club , rated the episode an A , calling it " utterly bad @-@ ass " . Handlen felt that the episode effectively toyed with the series ' usual narrative structure , making lead character Fox Mulder seem " nearly as much of an antagonist " as The Smoking Man ; Handlen also felt that " Zero Sum " gave significant insight into the character of Walter Skinner . Paula Vitaris , writing for Cinefantastique , rated " Zero Sum " one @-@ and @-@ a @-@ half stars out of four , noting that its " pacing and tone are off " . Vitaris felt that " Duchovny and Pileggi give good performances " , despite Pileggi seeming " unintentionally comic " at times ; though she noted that " an episode without Scully feels pretty empty " . Robert Shearman and Lars Pearson , in their book Wanting to Believe : A Critical Guide to The X @-@ Files , Millennium & The Lone Gunmen , rated the episode four stars out of five , noting that " Pileggi looks much more comfortable here than he did in last year 's showcase [ ' Avatar ' ] " . Shearman and Pearson felt that the episode 's attempts to tie into the wider storylines — the appearance of Marita Covarrubias in particular — are where it " really stumbles " ; noting that its success lies " in the shock value of seeing a deliberately familiar story through the fractured view of another character " . 
