With a very small adult size of about a cubic centimetre (1 cm3), they are both the smallest and one of the most venomous jellyfish in the world.

Robert Drewe describes the Irukandji jellyfish sting as "100 times as potent as that of a cobra and 1,000 times stronger than a tarantula's".

Irukandji jellyfish's stings are so severe they can cause fatal brain hemorrhages and on average send 50-100 people to the hospital annually.

https://en.m.wikipedia.org/wiki/Irukandji_jellyfish

There's also Cassowaries, possibly the closest thing you can get to the experience of being chased by the Jurassic Park velociraptors.

And the stonefish and conefish. Know where you place your feet!

Tasmanian Devils deliver the highest bite force relative to body size of all mammals.

But the whole species is under threat from the face cancer thing [0] Tassie devils are beautiful little nuggety marsupials. Their name belies their shyness.

[0]: https://en.m.wikipedia.org/wiki/Devil_facial_tumour_disease

they are many things but beautiful they are not. They may be shy but they're also very blustery as well. Thse WB animators probably never saw one but they got a lot right.

That’s harsh. They cute as cute can be. Right up until feeding time. Terrible terrible table manners.