Maybe, but sometimes people's tastes are different from others. It cannot be with only one form, it will create limitations. But your idea to give users reward maybe interesting to do, like if someone achieve an achievement, then there will be a reward for him. The reward could be in all forms, like free roll or another thing.
Excellent feedback! We do like the variance on the rewards, is there any other particular reward form you have in mind?
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I also don't know much about the various prizes, because what I often find are some free roll opportunities in the game, maybe you can see other sites for reference. Good luck