Spellskite, a new card from New Phyrexia, has an activated ability that allows you to change a target of a targeted spell or ability to the Spellskite itself. While it is possible to use Spellskite’s ability and target any spell or ability on the stack that can be targeted, Spellskite’s ability does not always end up changing targets. Spellskite cannot make the target of a spell or ability illegal. If when Spellskite’s ability resolves the Spellskite would be an illegal target, then the target is not changed.

One way that this can commonly happen is with equip abilities. Equip abilities can only target a creature that is controlled by the controller of the equipment. If your opponent is trying to attach his Darksteel Axe to a creature he controls, you can target this equip ability with the ability of your Spellskite. However, because changing the target of this ability to Spellskite would make this target illegal, nothing is changed. The equip ability will resolve as normal and attach to the creature that was originally, and more importantly, legally targeted.