
This should be fairly easy. Take a (Small) giant leech, reduce it to Diminutive, drop Aquatic subtype, modify slightly.
A scum creeper can move freely upon walls or ceilings due to its myriad tiny hooked legs and its suctioning underbelly segments.
Attacks are initially attempts to attach to the intended prey. A hit indicates that the scum creeper is fastened to some portion of the prey (1 in 20 will fasten the monster onto the face, blinding the victim until the monster is removed).
Rock salt rubbed on a scum creeper’s soft flesh causes it to suffer 2 points of damage per round for 1-4 rounds. (Additional applications are ineffective until the prevous saline effects are complete.)
They have only vestigial eyes and sensory organs in a cluster of cilia at the head.
That's a pretty good start.
It looks like this might be appropriate here:
Wallcrawling (Ex): The gacholoth need not make Climb checks to traverse a vertical or horizontal surface (even upside down). It retains its Dexterity bonus to Armor Class while climbing and opponents get no special bonus to their attacks against it.
I'm tempted to add a blinding/"facehugging" mechanic on a critical hit...
We can borrow this...
Salt Vulnerability (Ex): A handful or more of salt deals 1d4+1 points of damage to the leech on contact and causes it to detach itself from its victim.
It sounds like we can give 'em the blind trait (or myopic, at the very least).

Added to Homebrews.
I cut out the "can't breathe" portion of facehugging, as it's probably far too deadly for that CR range.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.