Sequential Wild Reels is a highly dynamic feature, primarily used in free spins bonus rounds, where with each spin, a new reel turns into or is added as a full 'Wild Reel' in a predefined sequence.
The core of this feature is to provide an experience of 'guaranteed growth', where the game board progressively accumulates wild reels as the round goes on, ensuring that the win probability and potential become stronger towards the final spins.