If I were to copy a card
Let's say something like oh idk
{Tormenting Voice}
With {Reverberate}
Would I have to discard another card for the copy?
I don't think so cuz you don't cast copies (except for things like Cipher)
But anyways yeah
Do you have to pay additional costs if you copy a spell?
You have already copied the spell, so you no longer get the opportunity to pay alternative casting costs, such as discarding a card.
In this case it's not optional, but if you copy a card with {reverberate} you needn't pay any costs of the original spell.
Damnit! I had a few opportunities to do exactly that with {howl of the horde} but I didn't because I thought you had to discard a card each time. Gotta remember that one