Antagonist
Character Role Analysis
Willie
Although the idea of Willie as antagonist is highly contestable—we don't actually know if he is going to shoot Winnie—it's still possible. Then again, killing Winnie could also be classified as a type of mercy killing seeing as how she's going to end up buried alive. Then again, again, there's the question that Mr. Shower/Cooker put forward: why doesn't Willie just dig out his wife in the first place?
Winnie
Winnie is her own biggest enemy. What's stopping her from digging herself out of the mound? If only she'd actually stop talking and "do something" (1.31), then maybe, just maybe, she'd get herself out of the mound.