The Drop Opener and Drop Closer
Begin by holding the closed butterfly pen by its free ends, with the hinge ends facing downwards along the base of your fingers. Pinch the ring in the end of the handle that is further from your wrist between the tip of the first finger and thumb. Next, open the rest of the hand slightly, allowing the pen to unhinge. As it does, quickly rotate your hand with a flick of the wrist to turn the palm face up, causing the free handle to swing up to join the one in your hand. Catch it to end with the pen in the open position, pointing downwards. Repeat these same motions to close the butterfly pen.
The Flip
This trick is done in almost the exact opposite way as the drop. In this move, the closed pen is now held with the hinges at the top and the ends pointing downwards. Grip the handle that is closer to your wrist between the thumb and the base of the fingers. Tilt the hand downwards (as if pouring a pitcher) and release the other half of the pen. Release the thumb's hold on the handle and regrip it by curling the fingers around it, then flick the hand back in the opposite direction. Stick the thumb out away from the hand to clear a path for the other handle as you give the hand a slight kick upwards, like flipping pancakes in a pan. Catch the free end as it swings up to join the held one to end with the pen in an open position pointing away from the body like a knife. Again, these same motions can be done to close the pen as well.
Double Flip
To perform a double flip, hold the butterfly pen in the same grip as with a single flip, with the hinges at the top and by the near handle with the thumb and fingers. Once more, tilt the hand downwards and release the other half, but, this time, instead of swinging it back into the palm, flick the wrist to cause the free handle to vault up and over the fingers and hang behind the hand. Now, flick the hand inwards at the wrist, allowing the held handle to spin 180 degrees within the grip and swinging the free end around the knuckles and back to the palm side of the hand. Kick the hand to flip it a second time to the back of the hand, then immediately bounce it back into the palm and catch it, rejoining the two halves.
Finger Roll Grip Switch
This trick starts out much the same way as a double flip by holding the butterfly pen with the hinges facing upward, releasing the further handle, then swinging it up and over the hand to rest on the back of the hand. While retaining grip on the former handle with the first finger and thumb, curl the other three fingers in and around to contact it on the other side. The handle should now be trapped by the index finger on one side, and the thumb, middle, ring and fourth fingers on the other. Release with the thumb and curl it and the ring and fourth fingers inward and out of the way as you turn the hand palm-downwards and swing the pen handle between the middle and first finger. As the free half vaults back over your hand and swings almost 360 degrees around your hand, regrip the held handle between the middle finger and thumb as you move the index finger behind it to join the others. Finally, flick the hand back to face palm-up and catch the free handle as the two halves join. At this point, the pen's hinges will be facing downward, in the opposite direction that you started in.