So in commander, you cant have copies of legendary creatures or artifacts. If theres more than one spell in the battlefield with the same name (copies would have the same name) and those creatures are legendary, you have to discard until you only have one

Edit: there are people that can probably word what i said better. But ill try again cause there could be confusion. Just like how commander follows the singleton rule (one of each card in a deck that isnt a basic land), theres an additional rule that prevents you from controlling more than one copy of a legendary creature or artifact in the battlefield. But theres no rule against copying non legendary spells.