General alternatives:
* Enemy: This is the most common and direct replacement for "foe."
* Opponent: This emphasizes the competitive nature of the relationship.
* Adversary: This implies a more formal or serious conflict.
* Rival: This emphasizes a competition for the same thing, often in a less adversarial way.
More specific alternatives:
* Nemesis: This implies a powerful and enduring enemy.
* Antagonist: This is often used in literature and film to describe a character who opposes the protagonist.
* Detractor: This refers to someone who criticizes or disparages another person.
* Opponent: This emphasizes the competitive nature of the relationship.
Informal alternatives:
* Bad guy: This is a casual and informal term.
* The enemy: This is a general term, often used in a political or military context.
The best choice will depend on the context and tone of your writing.