In a large bowl, combine the crabmeat, bell pepper, green onions, and water chestnuts. Add the egg, mayonnaise, lemon juice, wasabi powder, salt, and pepper, and stir gently to combine. Gently stir in the crushed crackers. Form the mixture into 12 equal patties.

In a large skillet, melt 2 tablespoons of the butter, and 1 tablespoon vegetable oil over medium heat. Add 6 crab cakes, and cook until golden brown, about 3 to 4 minutes per side. Repeat the process with the remaining 2 tablespoons butter and remaining 6 crab cakes. Arrange them on a serving platter. Garnish with red bell pepper strips to make spider legs, if desired. Serve immediately with the Mayonnaise Sauce.

Combine all of the ingredients in a small serving bowl.