In a large mixing bowl, add the pheasant, mozzarella, eggs, mayonnaise, flour, cornstarch, dill, salt, and black pepper and stir together until well combined. You can make the fritters right away, but if you have time, cover the bowl with a lid or plastic wrap and refrigerate for 2 hours, or up to overnight. This will give the pheasant more time to marinade, so you end up with fritters that are juicier and more flavorful.
Line a rimmed baking sheet with paper towels. In a large nonstick frying pan over medium heat, heat the olive oil. Working in batches, drop six 1-tablespoon portions of the pheasant batter into the pan. Use a spoon or spatula to flatten into 2-inch disks. Fry for 2 to 3 minutes per side until the bottom turns golden brown and the internal temperature reaches 160 degrees F using an instant read meat thermometer.
Transfer cooked fritters to paper towel-lined baking sheet. Repeat with remaining batter, adding more olive oil as needed. Serve immediately.
MAKE THE GARLIC AIOLI
In a medium mixing bowl, whisk together the mayonnaise, shredded celery, minced garlic, lemon juice, salt, black pepper, onion powder, and celery seed.
Serve the garlic aioli with the fritters or store in an airtight container in the refrigerator for up to 3 days.