n large plant 

Perception +12; darkvision

Languages Common, Elven, Sylvan (Can't Speak Any Language)

Skills Athletics +16, Stealth +12 (+18 in forests or swamps)

Str +6 Dex +1 Con +5 Int -2 Wis +2 Cha -1

Mound When it's not in danger, the shambler spends 1 minute settling into a pile that looks like a lump of loose vegetation. While it is in this form, creatures must actively Seek and succeed at a DC 22 Perception check (DC 28 in forests or swamps) to detect the shambler's true nature.

AC  22; Fort +17, Ref +11, Will +14

HP 120; Immunities electricity; Resistances fire 5

Electric Surge Whenever the shambler would take electricity damage or is targeted with an electricity effect, it gains 12 temporary HP and is quickened until the end of its next turn. It can use its extra action to Stride, Strike, or Swim.

Shamble [R] Trigger A creature unaware of the shambler's true nature comes within 10 feet. Requirements The shambler is in mound form. Effect The shambler makes a vine Strike against the creature. Then roll initiative.

Speed 20 feet, swim 20 feet

Melee [>] vine +17 (reach 10 feet), Damage 2d8+8 bludgeoning plus Grab

Vine Lash [>>] The shambler makes a vine Strike against each creature within reach. Its multiple attack penalty increases only after all the attacks.

Bestiary, page 290. Expanded in LOIL.