Score the fat cap on the pork butt and use a filet knife to poke holes throughout the meat to help the marinade penetrate. Season all sides generously with kosher salt and coarse black pepper.
Combine the orange juice, lime juice, lemon juice, minced garlic, oregano, cumin, onion powder, mint leaves, and zest in a medium bowl. Mix well. Remove ½ cup of the marinade and transfer to a separate container — this is your reserved mojo to be used when the pork is done cooking, and you don't want to add the oil to it. Add the ¼ cup of olive oil to the main marinade bowl and stir to combine.
Place the pork butt in a vacuum seal bag or large zip-top bag. Pour the marinade (with olive oil) over the pork and seal. Refrigerate overnight, flipping once before bed so the marinade redistributes evenly.
After marinating, remove the pork butt from the bag and discard the used marinade. Preheat your smoker to 250°F. Place the pork butt directly on the grates.
Smoke at 250°F until the bark is well developed and the internal temperature reaches approximately 160°F.
Remove from the smoker. Place the pork butt on several overlapping sheets of heavy-duty aluminum foil. Pour about ¼ cup of the reserved mojo marinade over the top. Wrap very tightly. Return to the smoker.
Continue cooking at 275°F until the pork butt is probe tender, approximately 200–205°F internal temperature.
Remove from the smoker and rest until the internal temperature drops to around 155°F. Do not rush this step.
Unwrap the pork butt carefully and collect the au jus from the foil. Shred the meat and mix in the remaining reserved mojo marinade (approximately ¼ cup). Add some of the au jus back in for moisture, adjusting to your preferred consistency. Serve immediately.