In a cocktail shaker, add in the gin, juice from one lime, and the acai powder.
Shake for 30 seconds until the shaker turns ice cold, and the mixture turns purple.
Fill two cocktail glasses with ice and strain the gin and lime mixture over the top.
Top the drinks off with tonic water and garnish with edible purple flowers (optional). If using dry ice, add to cocktail before serving.
Warning: If using dry ice, follow the manufacturer's directions carefully. Never handle with bare hands; always use tongs and gloves.
If adding dry ice to your cocktail, serve it with a straw so guests don't drink the ice.
If preparing for a party, you can pre-shake the gin, lime, and acid mixture ahead of time, and store in a container to serve later. Remember to put the ice in only when you serve, so you don't dilute the cocktail.