When I play Shadowblade Lurker from my trash, does it count itself for its cost reduction?
No. The first step of playing Shadowblade Lurker moves it from your trash to the chain, so that copy is no longer in your trash.354 The number of matching cards is checked afterward when its discount is applied, so only other cards named Shadowblade Lurker in your trash at that time count toward the reduction.356.4.g