Incendiary Caltrops (Patreon)

Wondrous item, uncommon

These caltrops contain a magical heat source at their center. A set of incendiary caltrops comes with 1d6 + 6 magic caltrops when found. You can use an action to throw any number of these caltrops in an unoccupied 5-foot square on the ground that you can see within 15 feet of you. When you do, roll a number of d4s equal to the number of caltrops thrown and record the total. When a creature steps into that space, it must immediately make a DC 13 Dexterity saving throw. The caltrops then explode, and that creature takes an amount of fire damage equal to the total rolled on the d4s on a failed save, or half as much fire damage on a successful one. Once a caltrop has dealt this fire damage, it becomes a nonmagical caltrop.

These little things bring to mind a conversation with my old adventuring group, on whether it was worse to face an assassin or a mage. With an assassin, you get the blade, a nasty bleeding wound, and damage that pierces deep. With a mage, you get flame, lingering pain, and raw, easily-infected scars.

But the simple answer is facing an assassin who is a mage, and I'm convinced that's who made these damned caltrops.