Complete Monster: The remnants of the civilization that exist on the "Intellivore" planet. They feed off of Life Energy, and though that's portrayed as not really their fault that they evolved that way, we later find out that the entities preserve the memories of the agonized deaths of every single person they've killed over the millennia. Why? Cause those memories are the most delicious.
Did Not Do the Research: Inaieu, the super-sized battlewagon, is said to be a "destroyer". Star Trek tends to follow 20th/21st century naval parlance, in which destroyers (from "submarine destroyer") are somewhere between frigates and cruisers like the Enterprise. (Then again, definitions do change over time: "frigates" used to be Ships of the Line.)