Guiding Bolt

At-will, std, ranged, DC 15; you shoot a guiding star at a target (spellcasting ability vs AC). If you hit, you inflict medium arcane damage. Whether or not you hit, the star hovers over the target for up to one minute. You and your allies gain advantage against the next three attacks against the target; three such attacks will end the effect.

While the effect remains, the star follows the target, moving up to 10 squares per round. It can follow the target is it runs, flies, or teleports, as long as the star has a path to fly to its new location. It cannot follow a target through water or under earth. If the target moves in a way it can't follow, it hovers in place, no longer granting advantage. But as soon as the target appears within 10 squares, you can direct the star back to the target as a free action on your turn. The star needs no vision to follow the target, so it can follow it even if the target is invisible or hiding behind total cover.