-the card say Action: Sacrifice a unit to have all units in your battlefield gain l until the end of the turn
if i play this the sacrifice unit have to be one of my or i can target my opponent uni ?
"Sacrifice means to remove a card you control from play." (FAQ, p. 10)
-"Festering Nurglings" Forced: After this unit enters play, corrupt one target unit in any player's corresponding zone.
can Festering Nurglings corrupt itself ?
Yes and it might have to. If you play FN into your Kingdom Zone and you nor your opponent have any other units in your KZs, FN is the only unit in play and must (since it's a Forced) corrupt itself.