Blue Ring Octopus

The blue ring octopus may be small and cute looking, but it is one of the most venomous species whose toxins can easily kill a grown man in no time. This octopus uses the same toxin, tetrodotoxin, for its self-defense as the puffer fish.
It packs another fatal one only for hunting. This other toxin is harmless to humans, but tetrodotoxin is so strong a single dose in can knock down 26 humans at the same time.
Brazilian Wandering Spiders

Brazilian wandering spiders belong to the genus of Phoneutria, which in the classic Greek language means ‘a murderess.’
Keeping in mind that these creatures are some of the most venomous spiders on the planet and it’s no wonder why the whole “family” is called by such an ominous name.
The wandering spider’s bite releases a whole cocktail of toxins, peptides and proteins which severely affect the neuromuscular system of the victim, causing critical heart problems and convulsions — even a very painful erection in men.
Hyenas

Hyenas have a widely accepted reputation of being scavengers, but there are some members of the hyena family that prefer hunting and killing rather than butchering found corpses.
Some can even go as far as killing and eating their own kind.These cannibal hyenas will not hesitate to attack and eat other hyenas when the opportunity presents itself and their hunger is peaking.
Even the youngest members of a hyena clan are not safe when their mommies and daddies get awfully hungry.