Grebner remains a bibliographic and historical puzzle. Apart from the ADB biography, one finds many brief references to Grebner, but few treatments of any extent. The one exception appears to be:
Åkerman, Susanna. “The Myth of the Lion of the North and its Origins in Paul Grebner’s Visions.” In Cultura Baltica: Literary Culture around the Baltic 1600-1700, edited by Bo Andersson and Richard Erich Schade, 23–43. Uppsala: Uppsala University, 1996.
Even tracking down Grebner's works is tricky, as his name is recorded in numerous forms, including Grebner, Gribner, or simply "Paulus Secundus" or "Paulus Iunior" (not to mention "Ezekiel Grebner, Son of Obadiah Grebner, Son of Paul Grebner"). There's a need for more work connecting Grebner's earliest published works in the 1560s to the manuscripts of the 1580s to the earliest pamphlets of the 1590s and early 1600s to their diffusion across Europe during the rest of the seventeenth century.
But it won't happen today. I still need to finish work on my SCSC conference paper, and posting may be sporadic for the next several weeks.