He can cast the following spells as natural abilities:
Detect Magic, Read Magic, Read Languages, Detect Alignment at will. Darkness, ESP and Locate Object X3/day Cause Fear and Putrefy Food and Drink, X1/day. Curse X1/week.
Unless restricted by a Magic Circle or bound by a spell, Grobbly automatically returns to his home plane within 3d6 hours after being summoned.
The basic outline of how to summon Grobbly is fairly common knowledge and is contained in numerous different grimoires in more or less accurate and complete versions. Magic Users and sorcerers are prone to call upon this foul thing primarily because this type of demon works for large quantities of meat, consuming 4d6 x 100 pounds of raw meat on average. Luckily, that meat can be in any condition, and come from nearly any source as the Grobbly are not very picky eaters. This makes them ideal first-time conjurings for would-be demonologists and summoners, allowing them to call forth something that probably won't automatically outwit them and demand exorbitant sacrifices, servitude and other such nonsense.
Once well-fed, the goblin will attempt to perform whatever task is required of it to the best of its rather limited abilities and notoriously deficient intelligence. Hopefully it will be able to complete the task before being returned to its plane of origin.
Grobbly is particularly well-skilled in locating lost objects and will often scratch a crude version of a treasure map into the floor or wall where they are summoned whether they are requested to do so or not. These maps invariably neglect to show any possible traps and often leave out important details, but they are always 100% accurate in terms of what they do show.