I have always loved Warhammer's take on goblins being "born" from mushrooms, and having no females among them, and releasing spores when wounded/slain so really there is no way to completely eliminate them as a species.
That being said:
34. Some tribes of goblins have a particular affinity for hags, treating them with respect and awe greater than that afforded their own high ranking shamans. They will refer to them as "grandmother" and bring them little trinkets and treats (including live captives). The hags, in exchange, only occasionally eat some of the goblins, and sometimes give their chieftans good advice (which always best serves the hags, but still).
35. There is a rare kind of mushroom - the trollstool - that can make a goblin stronger every time they eat one, but also makes them even more ugly, stupid, and violent than usual. After eating many trollstools, they may be so large and twisted that they could be mistaken for trolls; hence the name (that and the nauseating appearance of the mushroom itself). Sometimes goblins so affected can be controlled by their tribes, and other times they are driven away or killed after causing too much carnage. Some tribes forbid the eating of trollstools, while others revel in eating them whenever possible.
36. An underdark goblin named Pynch Toadbrew once stole a recipe for absinthe from a drow merchant, and experimented with it, creating a new spirit called "toadbrew". Toadbrew is similar to absinthe but contains warpstone, faerzress, or whatever similar substance exists in your campaign world, as well as other even less savory ingredients that involve, among other things, the capture of live faeries. It is a luminous, transparent green color, a clear glass of which sheds light equivalent to that of a candle. Toadbrew is extremely addictive and is known to cause spontaneous mutations.