Fluffy-tailed Hog

These usually appear together  in a pack of 2-3. In the Dune Desert they are mostly alone and in the Titan Forest in packs of 2-6. Beware the Alpha Hog which is much larger and takes more hits to kill. The hogs provide Alien Carapace when you kill them.

Lizard Doggo

A Lizard Doggo is an animal in the game that can be tamed and once tamed it will deliver items to you via an inventory slot. When killed it does not provide anything however if you put Nuclear Waste in the doggo's inventory before killing them the waste is removed from the game. A full article on Lizard Doggo's is available here.

Space Giraffe-Tick-Penguin-Whale Thing

A friendly creature in the game which is also a trampoline. Currently they are attracted to you and will annoy you by walking through foundations. They can be killed, it just takes a lot of hits and they provide Alien Carapace when you kill them.

Stingers or Cats

Stingers are another enemy in the game, although arachnophobia mode can be enabled in game to turn them into cats. There are three variants of them of different sizes and they provide Alien Organs when killed. The Arachnophobia Mode of the game allows them to be displayed as 2D cats instead.

Stingers Part 2

WARNING: Arachnophobia mode in the game has been turned off for this video so if you do not like spiders you may not want to watch this video.

Flying Crab

Another enemy in the game, one of the more frustrating ones. They hatch from a pod and that pod provides Alien Carapace.

Spitters

Spitters shoot fireballs at you, there are several different sized spitters and they have varying types of fireballs. They provide Alien Organs when killed.

Giant Flying Manta

The Manta is a large flying creature that can be found in two locations in the world. It cannot be killed however it can be ridden. For those who don't like clipping you will need to be aware of the Manta when building vertically, as shown in this video.

Non Flying Bird

Despite it's name this bird can fly short distances, it is a passive animal that provides nothing when killed.

Spore Flower

The Spore Flower is a creature in the world that will be triggered by movement and stand up to produce poison gas. It can be destroyed with a Nobelisk however it provides nothing when killed.