The secret to ensuring your venison remains tender and moist lies in the slow cooking process. It's crucial to keep the casserole covered throughout the cooking time to prevent moisture loss. Additionally, maintaining an adequate level of liquid in the casserole is key; this could mean occasionally checking and adding a little extra broth or water if necessary. Slow cooking at a low temperature allows the tough fibers and connective tissues in the venison to break down gradually, resulting in a melt-in-your-mouth texture that's both delightful and satisfying.