The Card Strengthening works like this You will need 2 cards that are the same and 2 other cards that can be used as Fodder for strengthening tho the effect are better when all 3 cards are the same. So in total, that's 5 cards you need the card your upgrading 2 cards that are a copy and 2 fodder cards. Strengthening has 3 stages before the card Tiers up. The 3 stages give minor benefits to the cards so let's take Fairy blast, for example, it gains 5 damage with each tier up but at the first tier up it's homing becomes stronger and it gains 15 more damage so it gains 15 damage from the stages than another 15 damage and an upgrade to the homing becoming minor homing which is a lot better. So at first tier, it has +30 damage and Minor homing. The card would look like this
