To show group headers see this example (build the &lt;thead&gt; element using colspan and rowspan).

To show borders around you group build CSS classes with border-left and border-right and use the columns.className option for the first and last column in your group.

Column Grouping with Title in DataTables
I understand that elites with the Avenger property get stronger as the others in the pack with that property die, but how exactly do they get stronger?

I'm looking for hard numbers.
