The guardian scroll is a very Harry Potter-movie kind of monster. I mean that very much as a compliment, both to it and the HP franchise. Before Sorcerer’s Stone, if you sprang a guardian scroll on the PCs your players would be like, “You’re attacking us. With paper. Yikes.” Post-SS (and especially post-Chamber of Secrets), it’s a lot easier to sell the image of a strangling, slicing, animate paper monster.
It’s also the kind of monster that has the potential to make PCs’ lives very difficult, irrespective of its CR. Nine times out of 10*, if PCs encounter a guardian scroll anywhere that’s not a moldering dungeon or pyramid, it’s because they are Doing Something They Shouldn’t Be—consulting the Forbidden Section of the library, sneaking into the College of Wizards, stealing from the daimyo’s painted scroll collection, robbing the Pirate King, etc. Perhaps the guardian scroll is a threat, perhaps not. But fighting off a guardian scroll is almost certainly going to be a noisy affair—one that will cause other interested parties to come running (preferably aimed with pikes and spells).
*The 10th time is when the PCs’ enemies send them a guardian scroll in an assassination attempt. Speaking of which, in a world where sepia snake sigils and explosive runes exist, it’s a wonder anyone even reads their mail.
The Shogun of the Brilliant Sunrise Prefecture is an avid collector of painted scrolls. He is also an avid employer of guardian scrolls, many of which fold themselves into gorgeous paper cobras, cranes, and chrysanthemums before attacking.
The priests of the Bookbinder are known for wearing linen scrolls as stoles that drape over their chasubles. Typically the scrolls are scribed with a sacred verse or a poem, and careful observers can detect praise, insults, or veiled warnings in a cleric’s choice of scroll. The high priests’ stoles are often guardian scrolls, which explains why priests of the Bookbinder have longer lifespans than many of their ecclesiastical peers.
Adventurers are sent a guardian scroll by an enemy. But as the scroll tube is not addressed to them specifically, they have the chance to pawn it off on someone else—assuming they suss out the nature of the construct within before it attacks. Forcing the enemy who sent the scroll to either open the tube himself or be publicly seen refusing to do so could win them prestige in the cutthroat world of court. That in turn could mean entry into the king’s intelligence service and/or lucrative charters to explore otherwise off-limits dungeons.
—Pathfinder Adventure Path #79 82–83 & Pathfinder Bestiary 5 138
The guardian scroll (including a more magical variant with spell-like abilities) originally comes from the Mummy’s Mask Adventure Path, which I rather dug. For one thing, it was an AP I got to enjoy as it unfolded. (I fell way behind my Paizo reading during Reign of Winter and Wrath of the Righteous and had to scramble to catch up, which is never as fun. I’ve had the same problem recently, so I committed myself to keep on track during Strange Aeons no matter where I was in Giantslayer/Hell’s Rebels/Hell’s Vengeance.) For another—and forgive me if I’ve mentioned this before, because I feel like I’m repeating myself—there’s a part of me that always resists pyramid/mummy setups because they’re so stereotypical, so it was nice to have an AP that executed those things so well I couldn’t help but be won over. (The undead invasion that kicked off the second MM entry went a long way toward achieving that.) Finally, after two or three APs that involved Really Big Stakes—the fates of Magnimar, Irresin, and the Worldwound/all of Avistan, respectively—it was nice to have an AP that kept it simple: stop a badass mummy. Sometimes you need a palate cleanser.