• Excessive cost of upgrades: The most significant example of this is the epic and rare primes, on this occasion I managed to upgrade thunder to rank 4 level 7 with only one million battle coins, the problem with this is the excessive increase of the cost in the last 2 levels.
Being that from level 1 to 8 only requires a little more than 2 million but from level 9 to 10 the cost is more than 6 million only for 2 levels. This really makes it not very convenient to raise the last 2 levels to the players, even collecting the battle containers and quests for battle coins is too excessive.