Combine first 3 ingredients in a bowl. Add beer, butter, and egg yolks, stirring mixture until smooth.
Pour oil to depth of 2 inches into a Dutch oven; heat oil to 375°. Dip sardines into batter; fry, a few at a time, 2 minutes or until golden. Drain well.
Stir together wasabi powder and 1 tablespoon water; stir in mayonnaise. Serve with sardines.