Game Mechanics: Random Uguk trains

[Striiker]

This is also happening in Blackburrow. We were fighting some gnolls near the commander room (but sufficiently far away from it..). All of the sudden we got stuff which must have been from the top level because we had Gnoll Pups agroing us along with a pile of others including the commanders, elites, etc.
We did have a bard in the group (and a druid and monk). This also happened randomly in other areas of the zone..