If an effect copies a card rather than a spell (such as that of God-Eternal Kefnet), this doesn't cause Ral's first ability to trigger. That ability will trigger if you cast the copy, however.

If an effect copies a spell multiple times, as Finale of Promise may, Ral's first ability triggers that many times.

If the spell that's copied is modal (that is, it says "Choose one —" or the like), the copy created by Ral's last ability will have the same mode or modes. You can't choose different ones.

Some spells instruct you to "copy target instant or sorcery spell." Because a spell is never a legal target for itself, you can't cast such a spell targeting itself to create a loop that causes Ral's first ability to trigger over and over.

You can't choose to pay any additional costs for the copy created by Ral's last ability. However, effects based on any additional costs that were paid for the original spell are copied as though those same costs were paid for the copy too.

The copies that Ral's last ability creates are created on the stack, so they're not "cast." Abilities that trigger when a player casts a spell won't trigger.

If the spell that's copied has damage divided as it was cast, the division can't be changed (although the targets receiving that damage still can). The same is true of spells that distribute counters.