Freaking out other players in Dark Souls 2 doesn't take much effort. All you have to do is stand there.
OK, OK, it's not exactly that simple. To pull off this prank, YouTube's GuardianHX dressed up as a Hollow Royal Soldier, went to the Forest of Fallen Giants, lured out the original foes, killed them and took their spot.
Then he waited for other players to invade, recording their double-takes and other uncomprehending reactions in the video above. At 3:50, you can see a perfect execution of the joke, though the ensuing fight does end in the perpetrator's death. (In Dark Souls, everything does, usually.)
This prank mimics one perfected in the original Dark Souls; this go-around is a little tougher because there the game applies more distinctive stances and animations to player characters. At a quick glance, though, it's still good enough to fool a lot of people.