Continuity mistake: At the beginning of the film you'll notice that when the blue creature from the ice chunk dives back into the water he has a tail fin. When the creatures attacks Manny and his gang and Manny shoves the creature off it dives back into the water again without a tail fin. Then at the end when Manny is attacked for the last time the blue creature has its tail fin again.
JadziaM
15th Sep 2015