Expanding Wilds Slots
An expanding wild grows from its landing position to cover the whole reel or row, substituting in every combination that crosses it.
How Expanding Wilds Cover the Grid
An expanding wild lands as a single symbol and then grows, most often stretching vertically to cover its entire reel. Once expanded, it substitutes in every combination crossing the covered positions, which on a ways-based grid multiplies all chains passing through that reel.
Expansion rules vary: some wilds expand unconditionally, others only when they can participate in a win, and some expand horizontally or diagonally instead of covering the reel. The order of operations matters and is defined in the rules, since a wild that expands before evaluation is worth far more than one expanding after.
The feature is most valuable in Ways to Win and Paylines games, where full-reel coverage bridges every row at once. It frequently appears inside Free Spins, sometimes in sticky expanded form, which merges it with Sticky Wilds behaviour.
Related but distinct: Stacked Wilds achieve similar full-reel coverage by landing as a pre-built stack rather than growing from one position, and Wild Reels turn the whole reel wild as a modifier without any landing symbol at all. The parent concept is Wild Symbols.