One down, on the Ground!

Airborn coffins are an affront to gravity. Use your equipment to avenge Mother Nature! About halfway through the cemetary, you'll come upon a large circular courtyard with a spooky tree in the center. When you do, immediately look up and shoot down a flying coffin. If you miss, you cab try again when the other two Black Slime Monsters pop up, or by replaying the mission later.