You create an echo that mimics your next attack with a weapon or spell in the following round with exactly the same roll and bonuses which you can then enhance in the following round.
Excellent for boosting 1 attack which will then be repeated in the following round.
Notice, however, that if the original attack fails, then the following attack also fails no matter what.
Your echo attack in the following round is done with a -20 penalty to the success rate unless enhanced. Thus, if you had an initial success rate of 130 on an attack with a weapon, that would be 110 in the next round.
The follow up attack does not cost AP - only the casting of the spell and the first attack costs APs.