I got the skeletons event, and took my small stack to attack two of them. As soon as I entered combat the game slowed to a crawl, but I continued playing. After taking out the first skeleton, Bannon Heighsley cast Slow on the second (appropriately enough). Summoned wolves had a turn, then my sand golem, then Bannon, again...and again...and again. All in all, he had six turns in a row, all with swarm.
When combat finished, the game was still going very slowly, so I saved and quit.