Well, to start with if u refering at the miscrits u get by prizes on daily, default and random arena, those are given with random ranks, so we ain't getting them with higher rank unless we are lucky enough, in case for miscrits in miscrit shop u have 3 options to buy, which are s+ that has a solid cost based on the rarity, same aswell with red speed but having a higher cost, and the low price for random ranks crits, which can be bought with the chance of getting any rank by a low prize