If desired, wipe rims of eight 16-ounce beer glasses or mugs with a lemon slice; dip rims in finely chopped crystallized ginger.
In a large pitcher, add the 3 tablespoons crystallized ginger. Muddle with a wooden spoon. Pour in fruity wheat beer and ginger beer; stir gently to combine. Serve in the chilled glasses or mugs. Top each glass with a scoop of vanilla ice cream; before or after pouring works, just be prepared for a little foam. Garnish with lemon slices.