Monkey See, Monkey Kill

All of the bosses and also the Protected Unga Keg can spawn randomly at all 4 different locations that are marked on the map with a skull once you start Stage 2.

- The Boat
- The Shipwreck
- The Isle to the northwest
- The Cave

Next to the bosses and keg there can also spawn a Unstable Keg, 3 Monkey's with brew and a Big Totem.

Above mentioned that the Protected Unga Keg was at 30,23, it can be there, but I got it on the Shipwreck, so confirming that this Protected Unga Keg also spawns randomly.

Took me about 5 Tries to get all of them.

I just confirmed that after finishing it, you still can look for the bosses, kill them and it still acount for the achievement.

Here's a tip for finding the [object=212278]. In my experience, it was not initially targetable, but spawned on of the the sand banks just off the coast at 29,22 on the scenario map. According to other commenters, it can spawn at other random boss locations as well, although I can neither confirm or deny this.

What tipped me off that I was in the right place was the presence of a bunch of [npc=62497] mobs in a circle surrounding a large keg (they were fast asleep). Killing off these mobs with some AoE was a fairly simple matter, thus making the keg interactable - it gave me a cogwheel and right-clicking gave me a bunch of brew and also completed that portion of the achievement.

Hope that helps!