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You cause a single natural opening or natural chamber to become animated. The opening or chamber cannot move, but it can attack. You can order it to attack any creature, or a specific type of creature. You also can order it to attack under a specific circumstance, such as when creatures try to leave or when they touch something.
An animated opening can only attack creatures that try to move through it. An animated chamber can attack every creature inside. Only one maw of stone can be in effect on a particular opening or chamber at a time.
The animated opening or chamber has a Strength score of 30 and an attack bonus equal to your level + your Wisdom modifier + 7 for its Strength. If it has any single dimension (height, length, or width) of 8 feet or more, it has a -1 size penalty on attack rolls for being Large.
An animated opening can make one grapple attack each round against a creature passing through. If it succeeds with its grab attempt, it makes a grapple check and deals 2d6+10 points of normal damage with a successful hold. A Large opening gains a +4 special size modifier and deals 2d8+10 points of damage.
An animated chamber works the same way, except that it can make a separate attack against every creature inside.
The animated stone has an Armor Class of 15, or 14 if Large (-1 size), and a hardness of 8. An opening has 40 hit points (60 if Large). A chamber has 60 hit points (90 if Large).