All of the competitors this round used the "short stat block" method to link to existing stat blocks in other sources. In most cases these links were to the Bestiary or one of the standard NPCs in the Game Mastery Guide. A few were a little more unorthodox: for example, one linked to a creature in a recent Adventure Path, and another linked to a creature in Burnt Offerings.
This sparked a bit of discussion among the judges, as if this were a print product, we wouldn't use a short stat block for a creature that wasn't in a "core" book--we'd either include the full stat block for a creature, or we'd change it to something for which we could use a short stat block.
Technically, the R4 rules allow the competitors to link to any material that's listed in the "allowed sources" section of the rules, and that includes "published content from Paizo's Pathfinder campaign setting," so all of these entries are valid, even though using a short stat block in this way is not something Paizo would do in a printed product. In future competitions, we're going to clarify our stance on this position. For this round, we're allowing it.
Because some of the linked stat blocks are in sources that aren't in the PRD, I've edited those submissions with spoilers at the bottom containing the necessary stat blocks (otherwise you wouldn't be able to playtest those encounters unless you had the books in question). To keep the competition fair, I've also added PRD hyperlinks to all monster short stat blocks in the Top 8 entries. Therefore, whether a competitor referenced a monster in Burnt Offerings or the Bestiary, that stat block is just a click away.
Keep in mind that the PRD doesn't have direct hyperlinks to variant monsters (such as fast zombies), so when following one of these links, make sure you know whether you're supposed to use the standard monster or one of the variants (as using normal zombies in an encounter that's supposed to have fast zombies may create a very different outcome).