Suppose that the effect of a monster like "Dragunity Dux" or "Dragunity Legionnaire" has its effect resolve and it equips itself with a Level 3 or lower "Dragunity" monster. If the effect of "Skill Drain" is then applied, then "Dragunity Dux" can no longer be equipped with a monster by its own effect, so the Level 3 or lower "Dragunity" monster equipped to it is destroyed and sent to the Graveyard.[3]
When resolving the effect of "Dragunity Dux", if the targetedDragon-Type monster is no longer in the Graveyard, then that monster is not equipped.[4]