Size & Type: Small-Huge Elemental (Water)
Space/Reach: Normal for its size.
HD: 2 (Small), 4 (Medium), 8 (Large), 16 (Huge), 21 (Huge, Greater), 24 (Huge, Elder)
Speed: 40', Swim 40'
Ability Scores (Small): Str +0, Dex +0, Con +0, Int -6, Wis +0, Cha +0 - Net -6, one penalty
Ability Scores (Medium): Str +4, Dex +4, Con +4, Int -6, Wis +0, Cha +0 - Net +6, one penalty
Ability Scores (Large): Str +8, Dex +8, Con +6, Int -6, Wis +0, Cha +0 - Net +16, one penalty
Ability Scores (Huge): Str +10, Dex +10, Con +8, Int -6, Wis +0, Cha +0 - Net +22, one penalty
Ability Scores (Greater): Str +12, Dex +12, Con +8, Int -6, Wis +0, Cha +0 - Net +26, one penalty
Ability Scores (Elder): Str +14, Dex +14, Con +8, Int -6, Wis +0, Cha +0 - Net +30, one penalty
Natural Armor: 4 (Small), 5 (Medium), 6 (Large), 8 (Huge+)
Natural Weapons: One Primary Slam (1d4 S, 1d6 M, 2d6 L, 2d8 H, + same dice of acid)
Skill List: Listen, Spot
Body Shape: Humanoid blob
Speech (Languages): Not noted, presumably no.
CR: 1-11
WotC LA: -
Our LA: -0 across the board
Immunity to acid, Improved Grab for one size category smaller than itself for its slam, and DR (5/- L+H, 10/- G+E). The acid damage from its slam also sticks around for a bit, forcing its victims to make a Fortitude save... that isn't based on any ability score and is therefore just 10+1/2HD... to avoid taking the same amount of damage again on the round after being struck. Dismiss Ectoplasm only stuns it for 1d4 rounds instead of the normal effects.
Finally, it can Envelop creatures smaller than itself, or two creatures that are at least two size categories smaller than it. The target gets a Reflex save (again, no attribute bonus to the DC) to avoid. Once captured, it can not physically escape. Each round spent Enveloped deals acid damage appropriate to the Ectoplasm Elemental's size.