Stir in the corn, onions, mushrooms, and green beans; cook 15 minutes more. Stir in the sausage; cook 5 minutes more. Add the crawfish, return mixture to boil, then simmer until the crawfish shells turn bright red and the tails pull out easily, about 5 minutes. Test for doneness by peeling a crawfish. Be sure not to overcook, or crawfish will become tough.
Drain well. Serve crawfish hot, Louisiana-style, spread over a picnic table covered with newspapers.