Pick 5 heroes to sacrifice as Materials. Only R, L, and L+ heroes can be used — L++ heroes can never be used as material. Each material contributes Score toward your Grade:
Your total Score (50–1000) maps to one of 21 Grades. Each Grade sets two separate things: the rarity odds for the 5 candidate heroes shown in your Dark Predictions, and the % chance each of the 5 slots ends up being your actual result. Candidates are always arranged worst-to-best across the 5 slots — the best heroes are placed in the last slots.
Higher Grades shift the whole rarity pool upward: R heroes stop appearing entirely past Grade 6, and L++ heroes can't appear at all below Grade 6. The other Grade to aim for is Grade 17, which removes all L heroes. Heroes selected as materials for rerolling will NOT be consumed until choice confirmation.
Add heroes you actually want to your Wishlist before rolling. As long as none of your 5 predicted candidates match your wishlist, you can re-roll the whole set of predictions for free — the RNG only really costs you something once you commit.
Once a hero you want appears, commit — the lab RNG lands on exactly one of the 5 slots (weighted by that Grade's slot odds) and that hero is your Result. Everything resets afterward. Landing on the hero you want is a chance, not a guarantee — seeing it among your 5 candidates doesn't mean the RNG will actually pick that slot.