Continuity mistake: Just before Steve Hadley is killed by the Merman, his tie is wrapped around his neck. When the Merman attacks him, his tie is worn properly. (01:19:40)
Continuity mistake: Before Dana and Marty enter the control room and release all the monsters into the control centre, there is a thermos flask and a torch sitting next to each other on the control room's desk. But once they enter the control room, the position of the thermos flask and torch have changed without anyone touching them.
Continuity mistake: When Curt is reversing the van from the crumbling tunnel, he's shown sticking his head out the window, then looking forward and again with his head out the window in the same shot.
Continuity mistake: When Lin is talking to Truman and says that they're all just letting off steam, the position of her hair on her left shoulder moves between shots.
Continuity mistake: This is just after Curt has jumped into the lake. The green towel around Marty's neck disappears and reappears. (00:22:00)
Continuity mistake: Aren't the survivors trying to escape by traveling through the tunnel in the same direction they took to arrive?
Answer: As you said, it is a satire of the common Deus Ex Machina trope you find in such films.