Valley of the Brain Collectors as a sandbox had plenty of optional encounters. However my players are very focused, it didn’t make sense to their practical hearted characters to disturb every nest in the Scar of the Spider. They stayed on mission. So they actually minimised and avoided contact with the inhabitants totally skipping the Cthulhu Mythos inhabited Fungal Cave. Here is the Color-Out-of-Space and the original Pathfinder version can be found here.
Huge ooze, chaotic neutral
Armour Class 7
Hit Points 72 (8d10 +24)
Speed 30 ft., fly 50 ft.
STR 16 (+3) DEX 25 (+6) CON 25 (+6)
INT 25 (+6) WIS 25 (+6) CHA 25 (+6)
Damage Immunities acid, cold, lightning, slashing
Damage Weaknesses force
Condition Immunities blinded, charmed, deafened, exhaustion, frightened, prone
Senses blindsight 60ft. (blind beyond this radius), passive Perception 8
Languages Aklo (cannot speak)
Challenge 13 (10,000)
Amorphous. The colour out of space can move through a space as narrow as 1 inch wide without squeezing.
Aura of Lassitude. A creature within 300 feet of a colour out of space (even when the colour is hiding within a solid object) must succeed at a DC 18 Wisdom save or become overwhelmed with listlessness and ennui. While under this effect, the creature has disadvantage on all Wisdom saving throws, and doesn’t willingly travel farther than a mile from the area where it failed its saving throw against that colour’s aura of lassitude. A dispel magic spell (or similar affect vs DC 18) ends the effect, as does removing the victim from the aura’s area of effect. Every 24 hours, a creature affected by an aura of lassitude can attempt a new DC 18 Wisdom save to cast off the effects of the aura. A creature that succeeds at this saving throw is immune to that colour’s aura of lassitude for 24 hours. A creature that is under the effects of an aura of lassitude from a colour out of space can’t be further affected by this ability from other colours.
Incorporeal Movement. The color can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn in side an object.
Legendary Resistance (3/Day). If the color fails a saving throw, it can choose to succeed instead.
Disintegrating Touch. Melee Natural Weapon Attack: +8 to hit, reach 5 ft.; one target.
Hit: 70 (10d6 + 40) force damage. It acts as the disintegrate spell under all other circumstances.
Feed (Recharge 5-6). A color can attempt to feed on any living creature or a region of plant life. Each creature in line of sight must make a DC 18 Wisdom saving throw, taking 1d4 levels of exhaustion. A creature killed by this affect crumbling into a mass of desiccated tissue.
An eerie radiance, a glow unlike anything else, suddenly suffuses the area, bringing with it a stifling sense of latent malignancy.