What happens when your players know every last classic monster in the Monster Manual, Monster Manual II, & even the Fiend Folio? This applies especially when you want to run something different in a retro clone mod like Dungeon Crawl Classics. Never fear we've got some monstrous options.
One of the biggest problems lately that I've found with OSR players? They know all of the classic monsters & many of the classic TSR era variations. Lately I've been slipping into Dungeon Crawl Classics rpg mode & while I have the option of using 3.0 & 3.5 D&D monsters converting on the fly is a giant pain in the behind. While Sword & Wizardry's Swords & Wizardry OE Reloaded: Monster Book is bloody brilliant & I highly recommend it. The monsters don't have the same punch when every player has a copy.
So what's a dungeon master gonna do?!! Well sometimes you've got to go back in time few years. In this case I'm pulling out the Teratic Tome By Rafael Chandler which has been free on Drivethrurpg the last couple of years. Rafael Chandler has been off social media since about 2018. He remains one of the more original OSR creators in my mind. Many of the monsters in this book are plane ending threats & fit the all or nothing view of monsters with certain OSR games.
Since I've been doing a lot of Castles & Crusades lately I've taken a very close look at how monsters are put together & there are a lot of classics in the Monsters & Treasure book. The Monsters & Treasure book for Castles & Crusades offers a lot of options but Teratic Tome By Rafael Chandler coupled with Monsters & Treasure is a perfect combination for an almost upper tier Swords & Sorcery or higher fantasy comic book style fantasy campaign.
While it seems that I'm getting away from Dungeon Crawl Classics, I'm not at all. The fact is that by combining these monster resources the dungeon master has an entire palette of mayhem to work with.
If I continue the thread of monster mayhem then I'd remiss to mention to the other other free monster resource by Mr.Chandler's Lusus Naturae a bestiary for Lamentations of the Flame Princess (and other old-school games). This book is an 'R' or even 'X' certificate monster book perfectly suited to vileness of some corners of the planes & other dimensions. These monsters are very twisted & have far reaching implications far past the dungeon & may affect a campaign on a very deep level.