When you use a Robot Master's Move that goes through an enemy when it makes contact with it, press Select as soon as it make contact. You will notice that the enemy flashes. When it stop flashing, press Select again then quickly press it again. The enemy will take damage again from the weapon! Use this as many times as you wish until the weapon is completely out of contact with the enemy. (Some weapons like the Ice and Electric ones work here. You may also use this glitch on Robot Masters for an easy fight)

In the video to the left, the player used it on the Yellow Devil.