Prospector Conall at Telredor wants you to kill Sporewing.
The first expedition the league sent reported encountering a gigantic spore bat they'd taken to calling Sporewing. They had to leave in a hurry, so they didn't have the chance to kill him while they were here, so I figured I'd finish the job for them.
What's left of their report suggests that the creature can be found in the southwestern parts of the Dead Mire. I think Vindicator Idaar mentioned that it's to the northeast of Telredor.