|You don't mess with him.|
Although lurkers are tied with hordes as the cheapest element in HotT at 1 AP, I think they more than pay for themselves this way. You spend one PIP to get them on the table, and if you place them correctly--attack the enemy's flank or rear so he's forced to turn out of his line or column--then even if you lose the close combat, your opponent then has to burn PIPs to bring his occupied elements back into the game. Not only that, but they serve as an intimidation factor, making an enemy think twice about moving his troops into bad going.
If a lurker loses a combat, it flees and can reappear in bad going elsewhere on the table. Sure, if it's doubled it gets destroyed, but hey, it's only 1 AP. And if you have more than one lurker, they can take down more powerful opponents if played right. One time I was playing my dollar-store spider army (12 hordes, 3 sneakers, and 3 lurkers) when an opponent's behemoth blundered through bad going. The lurkers popped up all around him, and with his -2 in bad going, plus the overlaps, he was down from a +4 to a 0 against my lurker's +2. Since he had enemies on his flanks, a loss in close combat would kill him--which it did. So lurkers, cheap as they might be, are also fun to play and can make a difference on the battlefield.
Bonus pic: The lurker element for my skeleton army, another Citadel figure.