Wow, it's been a while! So, I figured I'd make a few Subnautica creatures in Starfinder; partially to see how viable adapting the game to Starfinder rules is, and partially as practice making creatures in Starfinder.
I'll start with a simpler one, the Stalker, and go through the Alien Archive's steps, one by one.
Step 1: Array. Combatant; Stalkers are mostly about fighting. I'll also decide their CR here; I'm putting it as CR 2. They're not an insignificant threat, but they are usually the first aggressive creature players run into in the game, so I'll keep it in the lower ranges.
Step 2: Type. Animal seems like the closest fit. Magical Beast is debatable, but they don't have any supernatural abilities, so I don't think it fits.
Step 3: Subtype. Aquatic, if that wasn't obvious.
Step 4: Class. Skipping it. Not the best fit for Stalkers, or most creatures in Subnautica.
Step 5: Template. Skipping it. Also not a good fit. (Notes for the future: Should the Kharaa disease apply a template to the creature, not just a disease track? Or is a disease track the better way to handle it?)
Step 6: Special Abilities. This is the most open-ended step, as far as I can tell, so there aren't any easy choices here. Fortunately, Stalkers don't have any major special abilities; the only one I can think of is to give them a Metal-Hoarding trait, as follows.
(Metal-Hoarding (Ex) If a character uses the Handle an Animal task on a Stalker, they can gain a +4 on the Survival check by offering the Stalker at least 1 bulk of metal (even scrap metal) as part of the task.)
Step 7: Skills. Also gets more complicated. Their Combatant array grants 1 Master and 2 Good skills, while the Aquatic subtype grants Athletics as a Master or Good skill. Also, Alien Archive specifically repeats that these aren't set in stone here; varying the number of skills by 1 or 2 isn't a big deal. Personally, I'll put down Athletics and Perception as Master skills, and Stealth and Survival as Good skills for Stalkers.
Step 8: Spells. Skipping it; Stalkers don't have spells.
Step 9: Final Check. Crunch the numbers! The stat block I came up with is below.
Stalker CR 2 XP 600
N Medium animal (aquatic)
Init +2; Senses darkvision 60 ft., low-light vision; Perception +12
Defense HP 25
EAC 13; KAC 15
Fort +6; Ref +6; Will +1
Speed 5 ft., swim 50 ft.
Melee bite +10 (1d6+6 P)
Str +4; Dex +2; Con +1; Int -4; Wis +0; Cha +0
Skills Athletics +12, Stealth +7, Survival +7
Environment any aquatic
Organization solitary, pair, or school (3-6)
Metal-Hoarding (Ex) If a character uses the Handle an Animal task on a Stalker, they can gain a +4 on the Survival check by offering the Stalker at least 1 bulk of metal (even scrap metal) as part of the task.
Did I get any of the numbers wrong (or way off)? Can something be changed to make it better, either by Subnautica or Starfinder standards? What do you think?