Dark Vortex Slot by Yggdrasil Gaming

The bonus does not arrive on a scatter count. It builds in stages on the base 5x3 grid, and the staging is the whole engine. Two Portal symbols landing on adjacent reels turn those reels into Vortex Reels - five symbols tall instead of three - and lock them open for 3 spins. Each additional adjacent Portal that joins the cluster adds another Vortex Reel and 2 more spins to the timer. Two separate clusters can run in parallel, one on reels 1+2 and another on reels 4+5, which is where the 7-spin maximum comes from (3 for the first vortex plus 4 for the second). Run out of spins before all five reels have grown and every Vortex Reel collapses back to base height. Nothing pays out, the build resets.

What makes it tense is what spawns inside those open columns. Pink orbs appear on reels 1 and 5 only, blue orbs on reels 2, 3 and 4 only. The pool starts at 2 pink and 5 blue and resets every time the vortex closes. Each blue orb collected adds one spin to the eventual free-spin round, each pink one adds a wild to the stacked wild columns that print on the centre 3 reels. Trigger the round with no orbs banked and you get the floor: a handful of spins on a thin wild stack. Bank the full pool and you walk in with 5 free spins minimum and dense wild towers running through the middle of the grid.

The free-spin round itself plays on a permanent 5x5 layout with 3,125 ways evaluated from either side, the stacked-wild columns hammering the centre. Base-game ways math runs at 243 from a 5x3 footprint, with 3 and 4 of a kind paying from left or right and 5 of a kind paying from one side only. A Buy Bonus button on the bottom dock skips the whole orb-collection ladder for 80x stake and replaces it with two pick-and-click cards: the first sets your wild stack height between 2 and 10, the second sets your spin count between 5 and 20. The button greys out at coin values above €1, so high-stakes accounts have to grind it on the reels.

The cabinet sits inside a carved stone arch frame at night, candle finials on the corners and a magenta vortex churning behind the reels. High symbols are dark-fantasy creatures (vampire, witch, ghost, demon) and lows are runic card glyphs glowing in the same purple as the portal. When the orbs spawn they hover mid-reel as bright energy spheres, pink ones throwing sparks and blue ones glowing cold against the obsidian frame. 2018 release, and a relatively rare example from that year of a Yggdrasil ways game where the grid expands before the bonus triggers rather than during it.