diablo-3
I have never seen a legendary item drop from a treasure goblin, and am beginning to wonder if it's even possible for them to drop one.
Can Treasure Goblins drop legendary items? And does the type of Treasure Goblin matter?
I have read How do the Treasure Goblins work, however it does not address this question at all in either the question or the answers provided.
Currently, the answer appears to be no - if such a thing is possible, it's so extraordinarily rare that thus far nobody has encountered it and lived to tell the tale. However, it is possible to craft legendaries using plans found in Inferno - an expensive proposition, but as close to a vendored legendary as you'll likely be able to find.
Check out this post on Treasure Creatures.
Of note is the following graph that shows some interesting trends for the different goblin types.
It looks like the loot distribution depends on the name, not the color. Take this data with a grain of salt though, the sample size was fairly low.
Best Answer
Legendary items can be dropped by basically everything that's killable, lootable or that has a red border when moving your cursor over it.
Treasure goblin hunting is actually a popular method of farming legendary items alongside with chests and bosses.
As of now there are no 100% reliable statistics of what drop the most legendary items but I asked a friend of mine with paragon 370 (so I kinda think he knows some things when it comes to farming) and he told me that the most legendaries come from things in this order.
I myself haven't played as much as my friend did but i can say that I see a very similar drop rate when I'm playing.