Nobody actually knows. The ocean has never been explored to its fullest depths or lengths, neither has land. New life-forms are discovered almost on a daily basis. Mostly smaller creatures on land, but nobody knows what lurks at the bottom of the ocean.
The dangerous sea creature is the blue-ringed Octupus.
Sharks, killer whales and stingrays are all dangerous creatures found in the ocean.
Man
Piranna
Dolphins are not considered dangerous.
The black snake.
As always, the most dangerous creature found in the Sahara is man.
Oh, dude, the most dangerous "creacher"? Are we talking about some mythical creature or a typo for "creature"? Either way, I'd say the most dangerous creature is probably a mosquito because those little suckers can carry diseases and ruin your summer BBQs. Watch out for those tiny terrors!
No Dolphins in general are not dangerous to man.
i believe that is the Blue Ringed Octopus found commonly in Australia. and Yes they are dangerous there sting hurts a lot like A LOT!
The Shark
The most dangerous deep sea creature is the Sea Wasp. A deadly jellyfish. The slightest touch of their tentacles creates a permanent rash and horrible pain. Any harder and your toast.