The Donighal provides covering fire for Annabelle (to the extent she needs it, anyway; he knows she can take care of herself, but he also knows she can't be everywhere at once). He, in his turn, is just a leetle bit faster and more accurate than is humanly possible. And his fireballs are hitting harder, too; if any of his Elite targets stay attached to their torsos, it'll be a testament to Combine engineering.