So this movie starts off with an expedition to really deep in the sea. The diver/scientist lady gets attacked in the depths by something kinda resembling a giant black squid. After she's pulled back up and is looking through the damaged equipment (she was also fired from the diving project) she finds an egg.
She takes the egg and puts it in an aquarium in her basement. It hatches into a squid creature. She finds out it drinks blood and so gives it blood. Her and the creature like bond and she ends up feeding her boyfriend and sister to it. But the guy who hired her for the dive set the dive to find this creature, so she finds out it's like a sacred monster thing.
In the end it's put back into the ocean and multiplies. Ends on a scene of the ocean with tentacles. Saw it recently.