Grammatical correction
Original sentence: “At that instant, the mice scattered, leaving their king behind. With his army gone beneath the floorboards, the Mouse King lost the fierce look and went for nearest crack himself.”
- Comma splice / sentence clarity: The first sentence is a compound sentence that can stay as is, but consider combining for flow: "At that instant, the mice scattered and left their king behind."
- Consistency of tense and subject: The second sentence is fine, but adjust for parallelism: "With his army having gone beneath the floorboards, the Mouse King lost his fierce look and moved toward the nearest crack himself."
- Article usage: Add an article before nearest crack if you keep the original phrasing: "the nearest crack".
- Stylistic suggestion: You can improve readability by combining ideas: "At that instant, the mice scattered and left their king behind; with his army gone beneath the floorboards, the Mouse King lost his fierce look and moved toward the nearest crack himself."
Recommended final version (smooth and clear):
"At that instant, the mice scattered and left their king behind. With his army gone beneath the floorboards, the Mouse King lost his fierce look and moved toward the nearest crack."