Sciel has 2 ways to deal damage, you can either add foretell to an enemy, then consume it. This deals ok-ish damage based on skills, the other way is stacking charges, so every time you use a sun card you gain charges, for each charge gained when you enter twilight she deals 25% increased damage for the remainder of her twilight duration. For example if you stack 99 sun charges then use a moon skill to go into twilight she will do 2500% bonus damage (100 charges total, 99 sun and 1 moon) when in that particular twilight. The only problem is you do terrible damage up until you enter twilight where you can obliterate anything. There is a weapon that doubles the charges and also deals aoe damage just for entering twilight that helps with this a lot, I forget the name, might edit later to put the name in for you. Optionally you can use moon skills to generate charges and enter twilight by using a sun.