Fusing allows you to make a good card stronger at the expense of sacrificing an unneeded card. Generally, it is better to start with above an average card or cards that belong in Rare, Super Rare, or Super Rare+ tiers. When fusing cards of the same category (for example, Fire + Fire or Wood + Wood), you can get an additional experience point bonus. Also, if you have more cards that belong to the same type when you use it, there is a good chance of increasing the ability of your card upon fusing. Always use five cards for fusing to get the maximum evolution points for the lowest price. If you do not have five cards of the same type to fuse or you cannot add more because you already consumed all spare slots, just use any cards to fill up those slots. Instead of focusing on one at a time while fusing, try to fuse more cards in your deck. Having five starting monsters of all level 10 is better than having one at level 20 while the rest are at level 1. Do not fuse rank C or common cards, especially when they are under level 10. As you make progress, you will get lots of level 10 common cards. It is a waste of money to fuse cards that you will change or drop from your line-up later. Only fuse cards that you will use over a long period of time.