This means you can only cast them on your turn, during one of your two main phases, and only when there are no effects currently on the MTG Stack (about to resolve)
1/1 The One Ring The crossover between Magic and one of the greatest fantasy franchises ever was a significant milestone in itself, but WotC made it even more historic by introducing the 1/1 The One Ring
Unless you can find a way to bounce that card back to your hand and re-cast the other side, you're stuck with whichever one you played first
But what of the other serialized cards
Witherbloom, the Balancer (Borderless) Mythic, 288 So here we are with the final Elder Dragon card on this list, and its the second appearance of Beledros Witherbloom
Partial payments of the total cumulative upkeep cost cant be made