You could try with using 2 attachments, adding the “Trail” property to the character and positioning it near the arm.
Once completed, change the texture to what suits you. Ensure that when you wish to fire the Trail, it is enabled and then disabled upon request. If that seems to sharp, using TweenService you can tween the transparency of the trail to zero.
Make a part that is exactly like your hand or a cube with an offset to your hand, then weld it to the hand.
I have it in my game, if you want i will show you