Apparitions do not home to you or present any threat.
Targeting:
To focus on an apparition, hold right mouse button on a gem, and drag it down-left to set it to target special units.
To temporarily go "full bearing" attack on the apparition (or any other target, this is basic game function), select it. All towers that can attack selected target will lock on to it.
You will have an easier chance if you reposition your strong gems in anticipation of where it goes.
Weapon Choice:
Since apparitions do not have armor or healing, you can just spam fire as much as you can. They are subject to strike spells, so freeze them if you need time.
Barrage enhancement will not target apparitions, so if you need extra damage, use either bolt or beam.
Be warned that in GC2, your achievements are not "official" until you beat a level. You also cannot earn achievements during endurance mode.