Certainly! Generating test cases for a problem like "The Last Line of Defense" involves creating geometrical shapes (polygons), points of intrusions, and facilities. Here’s a Python function to generate such test cases:

```python
import random

def tcgen(): 
    # Number of polygons (1 to 5)
    num_polygons = random.randint(1, 5)
    
    # Generate polygons
    polygons = []
    for _ in range(num_polygons):
        # Number of vertices in the polygon (3 to 5)
        num_vertices = random.randint(3, 5)
        
        # Generate vertices (x, y) with absolute values up to 1000
        vertices = []
        for _ in range(num_vertices):
            x = random.randint(-1000, 1000)
            y = random.randint(-1000, 1000)
            vertices.append((x, y))
        
        polygons.append(vertices)
    
    # Number of occurrence points and important facility data (1 to 100)
    num_occurrences = random.randint(1, 100)
    
    # Generate occurrence points and facility locations
    occurrences = []
    for _ in range(num_occurrences):
        x1 = random.randint(-1000, 1000)
        y1 = random.randint(-1000, 1000)
        x2 = random.randint(-1000, 1000)
        y2 = random.randint(-1000, 1000)
        occurrences.append((x1, y1, x2, y2))
    
    # Format the output similar to the sample input
    input_data = []
    
    input_data.append(str(num_polygons))
    for polygon in polygons:
        input_data.append(str(len(polygon)))
        for (x, y) in polygon:
            input_data.append(f"{x} {y}")
    
    input_data.append(str(num_occurrences))
    for (x1, y1, x2, y2) in occurrences:
        input_data.append(f"{x1} {y1} {x2} {y2}")
    
    return '\n'.join(input_data)

# Example usage:
print(tcgen())
```

### Explanation:
1. **Number of Polygons**: Randomly choose between 1 and 5 polygons.
2. **Vertices of Polygons**: Each polygon will have between 3 and 5 vertices. The vertices' coordinates are randomly generated with values between -1000 and 1000.
3. **Occurrences and Facilities**: Generate between 1 and 100 pairs of coordinates representing the occurrence points and the facilities.

This should give a variety of test cases covering different scenarios and edge cases. You can run this `tcgen()` function multiple times to generate different test cases for your problem statement.