What you don't like or think doesn't make sense, you should change.
Description: You are more like the Shoggoths in Michael Shea's Fat Face than the ones in HPL's At the Mountains of Madness; your form and mass are not fixed, though you have spent a long time pretending to be some kind of humanoid.
If an Elder Thing tells you to do something, you have to save or obey; if a Deep One tells you to do something, you have to save or obey, but at +4 to your roll.
XP: Advance using the Halfling Experience Table; same level limit applies.
Saving Throws: Use the Halfling Saving Throw Table.
Prime Requisite: The Shoggoth class has no Prime Requisite.
Minimum Scores: No minimum as such, but you must reduce your other Ability Scores (1 for 1) to bring both Strength and Constitution to 18 (or as near as possible if you rolled low across the board). Reduced Ability Scores can only be taken down to 3, no lower.
Hit Dice: Either the highest Hit Dice used in your game (usually Fighter HD), or the next one up (so that the Shoggoth has the highest HD in your game), or d20 (because you think this Shoggoth isn't tough enough).
Armour: Shoggoths have natural armour equal to leather; their AC does not benefit or suffer from high or low Dexterity; they can wear any armour they want, but only benefit from a magic bonus or special properties; if a Shoggoth has a Dexterity of 9 or more, a shield can be used.
Weapons: Shoggoths can use any weapon, or use their natural attacks (which use a damage die the same as their HD).
- You only take half rolled damage from fire and lightning.
- You take only 1 point of damage (plus any magic bonus) from physical weapons.
- You regenerate 2 hit points at the end of every round, even at 0 hp.
- You can carry twice as much gear and treasure as other characters without becoming encumbered.