Moral Event Horizon: Ostensibly the blob crosses this line when it kills Joe. But then, no-one cares.
In Blobby's defense, Joe was beating his stepson rather severely, had threatened to break his neck and, in his drunken and enraged state, might actually have done so. Those who aren't openly attacking the blob's agents are dealt with non-lethally, and even when one of them tries to smash the blob with a rock, the blob merely destroys the rock.
Even Bud says, of El Blobbo's motives for killing Joe, "It didn't want Tim to get hurt." One might say it used excessive force...but then, it's psychic. Maybe it saw just how serious Joe was about hurting Tim....
Special Effects Failure: Whenever the blob emits a burst of light as part of its psychic attacks, it casts shadows of the actors and props on the "sky" behind them.