Considering they discover on average 14 new species of sea creatures every 2 weeks, I'm sure there will be some unusual creatures down there.

Something like this

I think the ocean floor is at the bottom of the ocean

Bin Laden and squidward

I mean maybe way way way way way way down there, like in a crack maybe 100 feet wide or so, leads down to a cave that is HUGE, equal to a large portion of the ocean we see today and down there are what we believe to be 'extinct' animals, Megaladons, all that stuff.

Well, roughly 70-75% of our World is made up of water so there is no chance we have explored the entirety of Earth's underwater mysteries. Personally, I only think there a few undiscovered species of fish but not much. Who knows though, there could be mega-megalodons for all we know? I suppose we wll never truly know, not in our lifetimes anyway.

There's no way there are still megalodon. They are so huge that someone somewhere would have seen one by now. Besides, they have the same lifestyle of a great white so they wouldn't be down that low. Mermaids are also a creature we would have seen by now. It's not like they are tiny little creatures that we may have missed.

Right at the bottom there would have to be some pretty insane creatures. Small fish couldn't take the amount of pressure of all the water, they would just and up getting crushed by the sheer pressure. That's why us humans have not gone to the deepest parts.

Ya for it to be able to withstand that much pressure would be crazy. It's a wonder what's really down there and how they withstand that much.

Alien life maybe but they would be blind or maybe atlantis.