Crocosaurus

The Crocosaurus is one of the titular antagonists of the film Mega Shark vs Crocosaurus. She is an ancient cryptid, a mutant cousin of the contemporary crocodile but blown up to gigantic proportions.

Mega Sharl Vs Crocosaurus
The Crocosaurus is encountered when a mining operation disturbs her cave. One of the miner initially discovers what he thinks are diamonds, however when he shows them to his overseer, the overseer notes that they are just very tough shell pieces. Shortly after the discovery, a gigantic crocodile shakes loose one of the mine's back walls and eats the overseer, chasing out the miners. Getting wind of the situation, the mining company hire famed hunter, Nigel Putnam, AKA "The Croc Guy" to clear out the mine. Going down to investigate, the mining representative is killed while on the expedition. News of the giant crocodile and gets out the the US military. Shark-expert, Lt. Terry McCormick is doing experiments on using sonic devices to repel sharks but is called in to try to help with the military's efforts to hold back the newly discovered Crocosaurus. Putman, McCormick and their joint-handler, special agent Hutchinson, are dispatched to try to stop the massive creature as it begins tearing up Orlando. All the while a massive aquatic cryptid, nick-named the Mega-Shark, has been reacting wildly to McCormick's experiments and has been attacks military operations. Before long the two creatures' efforts meet as the military tries to hold both off. As the Mega-Shark mostly remains a threat by sea, the Crocosaurus takes to the land, tearing-up Sea-World as a start.

Physical traits
As Putman points out Crocodiles have a semi-impervious hide, killing them often involves going at the from behind their heads at the weakest part of their scales, but even the Crocosaurus's weakest parts are still heavily damage resistant. As the Crocosaurus does not remain still, even getting one hit at the back the Crocosaurus's head is a challenge and ultimately not enough to seriously harm it. The Crocosaurus is large enough to squash a human with one claw, and big enough to break city walls. Tank-fire only seems to annoy the Crocosaurus at best. It's one weakness is electricity, and the military combat it with an Arc-Flash, however even a nuclear plant's Arc-Flash is only enough to stun it. As McCormic, Putman and Hutchinson discover late, the Crocosaurus has evolved to turn out eggs by the hundreds when/if her initial brood is destroyed.

Personality
The Crocosaurus is first and foremost concerned with her eggs. He initial attack is against those disturbing her nest and she immediately begins replacing and doubling-down on eggs when her first batch is destroyed. The Crocosaurus is able to track her eggs over vast distance and chases down the submarine that had taken one of her eggs for study. When the Mega-Shark develops a taste for the eggs and starts eating them, the Crocosaurus puts her rampage of Orlando on hold to attack the beast in an act of vengeance.