I’m wondering is there any guideline on how to create any creature? Or what traits/feats they can have?
Many thanks for the answers
Every GM is their own game designer ... over the past few years I've run into this a bit working on my own TTRPG.
First, designing creatures ... start with the combat basics and add behaviours and gloss.
Combat basics are: movement, attacks, defenses, and tactics... the basic "Stat Block"
How many zones, how much damage per attack, types of attacks, how much defense, types of defense.
This is kinda the most boring part and the part you don't really need to be fussy with... if you set out to tell the monster's story instead.
Tactics starts to get into behaviors ...
The Traveller RPG has a great abstract system for this - is the monster a pouncer? a chaser? etc.
How much morale / how fierce is the monster (and why?) ... is it defending a lair? Is it casually hunting and easily driven off?
Does the animal get enraged when first damaged? Does it get cagey? Does it run?
How does the animal use terrain/environment?
Johnn Four over at Role-Playing Tips / Campaign-Community.com has a whole mess of how to make cool animal encounters - not specifically for the ALIEN RPG but useful tips none-the-less.
One of his big ones from a course he offers called Faster Combat is to build a 3-round "story" around how your monster / creature / NPC / villain works.
What will they open with?
What will they amp up with when they see their first shot failed to win the day for them?
What will they use in desperation as the tide of battle turns against them?
When do they flee? (because not everything fights to the death every time...)
Another important consideration is *scaling* the combat to remain exciting regardless of how the tide of battle flows.
If the monster gets a lucky break in round one and pounds the party down ... maybe round 2 and 3 ease off a bit.
While you still let the dice do their job, there's a lot of other tricks and "sliders" you can adjust on the fly such as monster toughness and "hit points" without the players necessarily knowing.
Try to imagine the first 3 rounds of your animal encounter ... how capable are the characters at the start?
How much do you want or need to wear them down by the end of the encounter?
How many rounds max do you want the encounter to go?
Is this more of a random encounter or "action snack" or is this the big set-piece of the adventure that could last 10-12 rounds?
Action snacks - the monster takes their shots for 3-5 rounds, and are down ... incrementally wearing the party and possibly setting them up for a real challenge later.
Set-pieces are the climax that could be make-or-break, or life-or-death and may wear to the end.
So, analyze your players' characters and look at how much damage they can deliver, how much damage they can soak, and how much wear and tear you want to put on them in the encounter and scale accordingly.
This is part of why the starting stat block can be less important than it seems - because you can add in more or remove more ingredients on the fly as you run the encounter.
Monster too easy? It's got friends that appear in rounds 2 or 3 unexpectedly.
Monster too hard? Just drop its health to zero anytime needed for dramatic finish - the players shouldn't know to the decimal point how exactly tough anything is.
Maybe that earlier wound that didn't seem so great really was more awesome that it seemed in the moment... and was a killing stroke with a delay.
Tons more encounter, creature, and combat tips can be mined from his public article archive: https://www.roleplayingtips.com/archives/
Sometimes, however you just get stumped.
For that, a basic generator or checklist can help unblock the creativity.
The Worldshaker Creature Creator (Sadly LONG out of print and exceedingly rare to find) had 20 dice tables for creating a starting monster:
Here's one sample creature created from those dice tables:
BASIC SHAPE: Quadraped, long-legged like a giraffe
COVERING: a shell
PRIMARY APPENDAGES: flippers
SECONDARY APPENDAGES: hump or humps
PRIMARY BASIC CHARACTERISTIC: good hearing
SECONDARY BASIC CHARACTERISTIC: many parasites live in or stay on host
MAJOR CHARACTERISTICS: limited size change such as expanding bladders
ULTIMATE CHARACTERISTICS: immune to certain psionic power types (which?)
ENVIRONMENT: grassland or prairie dwellers
GROUP SIZE: extended family group such as monkey troop
NUMBERS: rare (therefore valuable?)
FOOD TYPES: photovore
TERRITORIAL ATTITUDE: territorial area large
PRIMARY MATING AND REPRODUCTION:
SECONDARY MATING AND REPRODUCTION: male dies after copulation
PRIMARY YOUNG CHARACTERISTIC: female suckles young
SECONDARY YOUNG CHARACTERISTIC: young protected unusually such as kangaroo
PRIMARY LAIRS/NESTS: makes use of natural nest or lair such as cave
SECONDARY LAIRS/NESTS: makes use of natural nest or lair such as cave
INTELLIGENCE: latent intelligence, recognizes food source, own kind, and is aware of surroundings, able to make priority judgements such as can assess danger, a
void enemies, etc
SIZE: tiny, mouse-sized
So, you can play 20 questions with those categories and see what you come up with...
Pressed for time? Do a web search for screenshots from No Man's Sky and try to explain any of those plants or creatures you see in your game...
We live, as we dream -- alone. ~ Joseph Conrad