Korlessa, Scale Singer

You'll still pay all costs for the spell, including additional costs. You may also pay alternative costs if any are available.

The top card of your library isn't in your hand, so you can't take other actions that would normally be allowed from your hand, such as discarding it due to an effect or activating a cycling ability.

Korlessa doesn't change when you can cast Dragon spells. Normally, this means during your main phase when the stack is empty, although flash may change this.