It might be understood as "Cuando venga a la misión..." too.
The only thing with "selempino" I came across is there at the very top of the 2012 03 17, 3:16 post; it's a site about the Legion.
"Selempino" (spelled "Selempinó" in the post at the link) can't be found wherever else I checked. I have no idea if there's any pun with "se le empinó" (= it raised [to him]).