Updated.
Spells don’t affect draggers, except as follows: magic missile inflicts normal damage; move earth causes the dragger to immediately depart for 14 turns, first releasing any prey not already swallowed; stone to flesh lowers a dragger’s Armor Class to 10 for the spell duration, immobilizing the creature if it is submerged in stone at the time (if only partially submerged, it can force itself out of the stone in 1 round at the cost of 2d4+2 hit points abrasion damage); stone shape can be used to force a dragger’s jaws through one involuntary movement and then hold it in the new position for the spell duration (in other words, to either hold the jaws shut or to force the dragger to open wide and disgorge a swallowed victim); and transmute rock to mud fully heals the creature (they otherwise heal 1 lost hit point per day, as many other creatures do).
Borrowing from some of the golems...
Immunity to Magic (Ex): A dragger is immune to any spell or spell-like ability that allows spell resistance. In addition, certain spells and effects function differently against the creature, as noted below.
A dragger is affected normally by force effects, such as a magic missile spell.
A move earth spell forces the dragger to drop any grappled or swallowed prey, then drives the dragger back 120 feet and deals 3d12 points of damage to it.
A stone shape spell either forces the dragger to drop any grappled or swallowed prey, or seals its maw shut (preventing use of its bite attack) for x rounds.
A stone to flesh spell does not actually change the dragger's structure but negates its damage reduction and natural armor for 1 full round, while immobilizing the creature.
A transmute rock to mud spell slows a dragger (as the slow spell) for 2d6 rounds, with no saving throw, while transmute mud to rock heals all of its lost hit points.
Skills: 11
Listen +5, Spot +6?
Feats: 3
Ability Focus (hallucinatory terrain), Alertness, 1 more?