Sure, I can create a test case generator for the given problem "Usagitobi". The generator will create random values for the grid size and the jump parameters while ensuring they fall within the specified constraints.

Here's the test case generator for the "Usagitobi" problem:

```python
import random

def tcgen_usagitobi():
    # Define the constraints
    min_val = 1
    max_val = 100000
    
    # Generate random values for m, n, a, b, c, d within the constraints
    m = random.randint(min_val, max_val)
    n = random.randint(min_val, max_val)
    a = random.randint(min_val, max_val)
    b = random.randint(min_val, max_val)
    c = random.randint(min_val, max_val)
    d = random.randint(min_val, max_val)
    
    # Return the generated test case
    return m, n, a, b, c, d

# Example of generating a random test case
test_case = tcgen_usagitobi()
print(test_case)
```

This function `tcgen_usagitobi` will generate a random test case, ensuring all the values are within the valid range. You can call this function multiple times to generate different test cases for your competitive programming problem.

If you need to generate a large number of test cases or save them to a file for further use, you can extend the script as follows:

```python
def generate_multiple_test_cases(num_cases):
    test_cases = [tcgen_usagitobi() for _ in range(num_cases)]
    return test_cases

# Generate 10 random test cases
num_cases = 10
test_cases = generate_multiple_test_cases(num_cases)

# Print the test cases
for case in test_cases:
    print(case)

# Optionally, save the test cases to a file
with open('test_cases.txt', 'w') as f:
    for case in test_cases:
        f.write(' '.join(map(str, case)) + '\n')
```

This script will generate 10 random test cases and print them out. Additionally, it writes the test cases to a file named `test_cases.txt`, with each test case on a new line.