Instructions
Press the space bar to jump.
Double-tap the "W" key to dash forward. Alternatively, double-tapping "A," "S" or "D" can be used to dash left, backward or right, respectively.
Click the mouse button to slash.
Press the "Shift" key to block.
Combine all of the moves quickly to perform a Butterfly. The order is jump > dash > slash > block. Practice the moves until they blend together. Start out performing each move slowly and then progressively increase the speed at which you press the buttons until the sequence becomes seamless.
Alternate the dash direction so that you may practice going in a direction other than forward. Once you get a handle on the timing for the Butterfly, you'll be able to travel around the map quickly while using the move.