give accessories bonus when attached ( for example goggle increase range size for gun , angelic wing give you movement speed increase , canteen give 1 extra health pill ..etc , I am sure knights will be happy to pay for these accessories to boost their combat stat ). also armors, shields, weapons , trinkets and accessories will have durability bar that when it's broken , it need to be repaired by some artifact found in lockboxes?
every 7 boxes opened will give one chance to re-roll ( exp : you open 7th lockbox and find a cool side blade , then there will be 2 buttons to choose , 1 is "accept item " the other one will be "roll again"
And so begins the power grind system prevalent in many other cashshop games.... and making them degrade is the extra kick in the nuts. Theres a good reason costume items never gave players bonus stats, and the sheer number of accessories you can attach would unbalance this in an instant.