Lightly dust thighs with salt and pepper and sear on grill or in skillet (heated to 400 degrees F) to caramelize the exterior.
Add grilled thighs to the slow cooker and set to low. Add 1 red bell pepper, 1/3 cup Coca-Cola, and 1/2 cup pheasant stock.
Finely dice half of a medium yellow onion and caramelize in a skillet. Do this by adding a light coating of oil to the skillet and set heat to medium-low. Lightly salt and pepper and stir often for 20-30 minutes until onions are soft and dark brown. When onions are caramelized, add them to the slow cooker.
Braise thighs in the slow cooker for 4-6 hours, until meat falls off bone. Shred and remove all traces of bones and tendons. Turn the slow cooker to Warm once the meat is shredded.
To make the mango salsa, dice the mango into 1/4- to 1/2-inch chunks. Mangoes have a thin, football-shaped pit in the middle. Use a good vegetable peeler or sharp knife to slice off the skin, then cut off from the pit in sections and dice.
Heat a small saucepan on medium-low and add 1 tablespoon of salted butter followed by the diced mango. Dust with kosher salt and freshly cracked black pepper, then add 1/2 teaspoon Sambal chili paste, 1/4 teaspoon cumin, and 1/4 teaspoon ground white pepper.
Stir often until the mango chunks are mostly soft. This may take approximately half an hour or so.
Fry six corn tortillas in thin layer of sunflower oil (or comparable cooking oil, not olive oil) on both sides until crisp.
Add shredded thigh meat to tacos and top with the mango salsa. Garnish with freshly minced cilantro.