Got this one about four or five times so far. The way it works the sprout spawns at the spot you're suppose to go to. Four dark enigmas spawn at four points around it just outside of the ruins and move to attack the sprout but can also attack each other. You are expected to get credit for three out of four of those kills while keeping the spout alive then you get a new mission to check on the enigma sprout. This is a find/tag mob type and yes it does only last a minute or two at the most. If that times out you then get the kill three dark enigmas mission again.
Also the wait time between spawns is about twenty minutes. One time I came with two chars within team range of each other, started to buff up then along comes a 220 with a lowbie. The lowbie goes to the spot, the 220 insta kills the dark enigmas then they fly off. I then had to stand around for about twenty minutes before another batch would spawn.