Here's my take on the creature, hinted at at the start of the "It's my Birthday, too" short story.
Slime Golem
High Concept: Animated slime “construct”
Skills: Alertness Fair (+2)
Athletics Good (+3)
Endurance Good (+3)
Fists Good (+3)
Might Good (+3)
Weapons Good (+3)
Stunts: No pain, no gain: You may take an additional minor physical consequence
Powers: Breath Weapon [-2] (See below)
Supernatural Sesnse [-1] (Tremorsense)
Gaseous Form [-3] (Liquid)
Inhuman Strength [-2]
Mythic Recovery [-6]
Physical Immunity [-8]
Stacked Catch [+8] The golem is immune to physical damage (unless a relevant maneuver or consequence such as Brittle or Solidified can be tagged or invoked.) Otherwise, the golem is vulnerable to energy such as fire, electricity, explosions, etc. Unless destroyed utterly, it will regenerate by drawing moisture and energy from its surroundings.
Stress: Mental
Social
Physical
Total Refresh Cost: -15
Notes: When using the Breath Weapon, the golem releases a torrent of slime on the environment. The targeted zone gains the aspect Covered in slime, as does anybody hit by the attack. Anyone struck by the weapon (or a physical blow from the creature) again while Covered in slime enters a grapple with the creature. Breaking out of the grapple requires meeting the catch or waiting out the duration of the maneuver; when separated from the golem, the slime will quickly dry.
Otherwise, fair initiative, Weapon:2 fist attacks and strength, and it can “see” you through the ground. It can turn liquid to pass through tight spaces or slip away under cover, and is guaranteed to return in top condition. Blast it hard enough and it can’t recover.
I wasn't really sure how to handle the "breath weapon." This seemed like the best way, but perhaps there are were better ways, too. The creature doesn't represent much of a threat initially, but it's major threat is the ability to escape easily, regenerate, and come back ready to fight, which is pretty much what I imagined the problem would be with such a creature.
