Stony-Faced
The Stone fish, as the name says, has a rough and rock like exterior which easily can misguide you. They live in and around coastal areas of the Indian Pacific Ocean. If you disturb them, you are likely to get affected by its neurotoxin for which an anti venom is needed.
Strangler Octopus
Now this one is deadly! The Blue ringed octopus attacks if it feels under attack. The poison paralyzes respiratory muscles and that is a mortifying thought. This creature is found in the Indian and Pacific oceans and is also known as the most poisonous in the blue sea.