Dwarf Mine Slot by Yggdrasil Gaming

Three Bonus runes on reels 1, 3 and 5 push the cabinet from four rows tall to seven, and that same trigger doubles as the gateway to the 10-spin Free Spins round. Each rune adds one row to the bottom of the grid - one Bonus gives 5x5, two gives 5x6, three gives the full 5x7 with all 16,807 ways live and an immediate trigger into Free Spins. Symbols on the new bottom rows drop in at random, so the spin that lands two Bonuses still gets a fresh evaluation across the expanded ways before any wins resolve.

The other rule running in parallel is the Crystal Collection, four meters sitting just left of the cabinet tracking green, yellow, blue and red gems. Crystals only appear on the bottom three rows of the expanded portion of the reels in base play, which means a non-expanded 5x4 spin produces no Crystals at all. Each colour fills its own counter at 5/5 and triggers an independent 5-spin Collection round when full. New accounts arrive with three reds already credited, so the first red bonus tends to land within the opening session and the longer chase is for greens.

Multiple full collections resolve in a fixed order - green first, then yellow, blue, red - and if a Bonus-triggered run and a Collection run fire on the same spin, the Bonus 10-spin round plays first. Inside Collection Free Spins the math reshapes. The grid stays at 5x7 for all 5 spins, no further Bonus or Crystal symbols land, and a super-high pay symbol matching the collected colour gets seeded into every reel. That symbol pays from just two on consecutive reels. Collection spins also use the average coin value of the spins that contributed each Crystal, not your current stake, so dropping bet size after filling a meter doesn't shrink the payout.

No wild lives on the reels. Reel expansion plus crystal collection do all the heavy lifting, which is unusual for a 2019 Yggdrasil release and makes the chase feel less like waiting for a high-volatility blowout and more like steady meter management. The art commits to that mood. A wooden cabinet braced with iron brackets sits inside a stone mineshaft, a bearded dwarf leaning against the right pillar holding an oil lantern, dwarven tools (pickaxe, hammer, chisel, helmet lamp) for highs and carved-stone card suits in red, blue, green and gold for the lows.