i've recently edited the source of spider web following martin's mod
http://rathena.org/board/topic/53901-how-to-make-spider-web-works-like-ankle-snare-and-soul-link-that-adds-max-hp/
edited it a little.
the spider web will be target to the ground and act as a trap, so when a player steps on it , a timer that restricts a character's movement (can't move but can still use skill) . i'm missing a mod where, when Landprotector is casted on the spider web it also removes the status timer