Borderlands' Tiny Tina DLC is now standalone and free from the Epic store
Tiny Tina's Assault On Dragon Keep was originally a Borderlands 2 DLC, but now it's available as a standalone release called Tiny Tina's Assault on Dragon Keep: A Wonderlands One-shot Adventure. It functions as a taster of what's to come in its successor, Tiny Tina's Wonderlands, due next year.
While Dragon Keep will cost monies on Steam, it's available for free on the Epic Games Store for a week.