The Living Web uses a special (aka homebrewed) extraordinary ability called Webball...
Webball (Ex) A Living Web may, once per encounter, has the ability to compress itself into a webball and roll along the ground at a great speed. It can move up to 60 ft. as a full-round action. At the end of the move, the Living Web ooze bursts back to its original size.
Any creature that now occupies one of the Living Web’s spaces is either pushed back, as if they saved against its Web Engulf ability (no action required) or can stand their ground and remain on top of the Living Web (an immediate action*). A creature that stands its ground must must a DC 17 Reflex save or be engulfed by the ooze. If the creature remains on top of the Living Web in subsequent rounds, they must save each round or be engulfed.
Like with Web Engulf (see below), a creature that stands its ground may make an attack of opportunity against the Living Web ooze, but if they choose to do so, they do not get a saving throw to avoid being engulfed.
The deadly nightshade is cocooned in the webball until the Living Web ooze stops moving. The nightshade acts normal on its turn in the same round.
*A creature that has already used a swift or immediate action in the round cannot choose to stand their ground.