If a wish can go wrong, a glabrezu will make sure it does. These creatures are the ultimate tempter demons, specializing in monkey’s paw wishes with truly horrid consequences. They’re also fierce combatants—Huge, four-armed, and with spell-like abilities that don’t just hurt, but also wreak havoc when employed (chaos hammer, confusion, power word stun, reverse gravity, and the ability to summon vrocks or another glabrezu). And they’ll answer planar ally or planar binding spells if the opportunity is sweet enough, meaning PCs could wind up facing them anytime they make a powerful enemy.
After losing the trail of a gelugon, some knights are approached by the ice devil’s direct rival, a glabrezu, who offers to serve as an adviser and guide. They know the demon will turn on them at some point but the intelligence he offers is at first glance invaluable.
Adventurers are forced to turn to a glabrezu to raise their dead friend. At first, they think they have crafted a loophole-free wish—right up until the moment a marut shows up, convinced their friend’s soul must be returned to the Beyond. The adventurers must choose to flee or fight, neither of which will be easy once the treachery demon and his summoned vrocks join in, pitting both the forces of Law and Chaos against them…at least for a few rounds, until the marut can be convinced to relent or the demon’s discipline breaks and they attack the hated inevitable.
An efreeti malik and a glabrezu square off in a duel of wishcraft. After some haggling over the terms (the genie limiting himself to three wishes a month within the city of the duel, versus the glabrezu’s one), they each choose a mortal to tempt, the goal being to create as much tragedy as possible. Both are bound to cheat of course—the demon with summoned allies, the genie with wishes cast just outside the duel’s confines—and after only a few months of this game, the cumulative horrors from wishes gone awry begin to mount.
—Pathfinder Bestiary 61
As usual, James Jacobs has a bit more on the glabrezu in Book of the Damned, Vol. 2: Lords of Chaos.