I am currently running a campaign in Athas (Dark Sun world) and I sometimes want the adventurers to face some specific monsters that would fit the situation. And, to my surprise, even with three Monster Manuals, two Monster Vaults, and other books with monsters, I don't find everything that I need.
Usually I just make some minor adjustments and re-skinning of some monster and that fits just well into the game. But other times I have to mix and design new abilities and attacks that I imagine the creature having. And that is the case of the monster and NPCs I will post on these articles I shall name "Homemade Monsters".
The first two creatures I will be presenting are the "Giant Desert Scorpion" and the "Blood Bat Swarm". They were both made for an adventure I ran on my Dark Sun campaign.