Fusion occurs when a duplicate card is acquired.
You can fuse cards by earning the card again through challenges, Battle Mode, Faction Wars, through Kard packs, or by purchasing the card directly through the store. If you purchased the card directly through the store, then the fusion will happen automatically. Otherwise, you can fuse the card after obtaining a second copy by opening your card Kollection and tapping the card to view the back of it.
Still have a question? You can submit your question here. You can also update and track your ticket as well.