If your query was instead for a literal academic paper with "Undying" and "v0.5.1" (or similar versioning):

It is critical to install "Fixpacks" (like the BG2 Fixpack ) before quest mods to avoid game crashes.

The request for "download-undying-v0-5-1" likely refers to the (v5.1 or similar), which is a component of the Baldur's Gate Quest and Encounter (BGQE) mod. 📄 Key Resource