Hey I'm back. Today I have a fun topicm and probably my most fun topic ever in my opinion: Brainstorming Creature and Monster Ideas! At this point of my pixel art journey, I have drawn a ton of pixel art monsters, starting with GIMP, then moving over to Graphicsgale, and today I use Aseprite for all this stuff.
Some Aliens I Drew
I drew various small alien creature sprites years ago on Pixel Joint (back in my amateur days, yes). This was the original batch I sketched out, ripped directly from my abandoned Pixel Joint account:

Then last night I was just passing some time by scrapping the ones I didn't like as much but also tweaking some of the better ones:

The Inspiration
Now, I didn't come up with these ideas purely on my own. Ratchet and Clank was a huge part of my gaming childhood, and I'm glad that the video game series has released so many games up to this day. Why? Because they have created so many fun and goofy alien and robot characters and enemy designs as a result.
The big artist (or at least a big artist) that played a huge role in the art of Ratchet and Clank games was Dave Guertin. He was the main concept artist for Ratchet and Clank games ever since the first game was in development, and here are some of his alien and artworks.


Brainstorming Your Own Creatures
I have a process to come up with wacky creature and monster ideas, but a lot of this is derived from existing visual inspiration. A great source of browsing and gathering inspiration is Pinterest. Pinterest allows you to browse any category of creatures such as demons, zombies, golems, ghosts, orcs, trolls, goblins, dragons... the list goes on, but yes also aliens. The key difference between searching for images on Google and Pinterest is that Pinterest let's you save pins to board (essentially bookmarking your favorite images for future reference). I suggest you try it out because it's free!

Deconstructing Visual Features
I don't know if anyone remembers playing Spore Creatures...





That game let you design creatures as weird, and bizarre, and disturbing as much as you could ever want, but the point I want to make is that in that game creatures would start off as a simple shape (for example, a sphere blob if I remember correctly), which you could then add and remove features from, such as eyes, hands, feet, tails, fins, bug legs, etc.
Mentally Deconstructing Creatures Into Smaller Features
Now that I mentioned Dave Guertin's various alien designs, Pinterest, and Spore Creatures, I want to talk about deconstruction. Creatures are "constructed" from various smaller visual features. They are just assembled together (like LEGOs TM).

Design Freedom
Unless you're drawing a trope, you have full freedom to draw whatever creatures you want. You can always decide what features you want to include, but also what features you want to exclude, allowing for a pretty much endless combination of creatures.
Tropes Have Some Rules
There is a small caveat when it comes to trope monster categories however. Trope monsters have rules, which serve as design constraints you must (or at least generally should) follow to draw the monster. For some examples, a dragon must have wings, a skeleton must be made of bones, a zombie doesn't need decaying flesh wounds, but it probably should, etc.
Think Critically Instead Of Cliche
Although some creatures have contraints by their definition. You often still have some design freedom. Think critically about if they must have certain visual tropes or not. Ask yourself "Does it always need to look like that?", because sometimes the answer is "No, people just make it look like that a lot.". A dragon (or wyvern) typically has 2-4 legs, but maybe try 6 and give it 4 eyes or even 4 wings. A skeleton can have a big blue magical soul orb protected within its rib cage. A zombie can have poisonous blisters or fungi ready to explode upon death. Try to not constrain yourself too much whenever possible.
Some Things You Can Practice First
If you're terrible at drawing, try drawing in grayscale first and try small sprites that are about 32x32 or 64x64 pixels. You can also try just directly drawing fan art of some of your favorite monsters. For example, one of the things I did early on was practice drawing chibi-sized Final Fantasy monsters. This way you don't have to think so hard about "designing" but can focus on improving your general pixel art skills first and get used to drawing various monster features this way. These early general drawing skills will become second-nature over time and practice.

A Few More Of My Monster Examples
Then once you become great at that, you can practice imagining your own stuff and even upscaling your sprites if you're up for the challenge!
"Halloween" Creatures

Demons

"Meatball Zombie"

Anyway so those are my tips for drawing monsters and creatures in Aseprite. I hope this inspires you and remember to have fun. Thanks for reading!