system explanation

First of all, I would like to say that I am not an American, so I can get it wrong about how US policy works, if I get it wrong, please help me and I will correct it. Obviously I did some research, but I can make mistakes.

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The system is very simple, it has 3 types of roulette, the common roulette that can spin 3 times a month, the epic roulette that needs an epic key that you win in the missions and the legendary roulette that needs a legendary key that you win mission victories.

The strength level of the item or character are these;

(-F) = Very low impossible to calculate

(F) = Garbage

(E) = bad

(D) = weak

(C) = whatever

(B) = good

(A) = Strong

(S) = Very strong

(SS) = legendary

(EX) = impossible to calculate because it is too strong