Reign of the Mountain King Slot by Light & Wonder

Everything here points toward one feature. Land a wild on reels 2, 3 and 4 in the same spin and the Mountain King Respins start. Those three wilds lock in place at x1, the rest of the reels respin, and any fresh wild that drops on the centre three columns locks too. The catch is the edges: a wild on reel 1 or reel 5 still sticks, but it carries no multiplier, so the value lives strictly in the middle of the grid.

The multipliers come from the gem trail running above the reels. Gem symbols that land during the feature slide up onto the trail, and every third gem collected pushes the current wild multiplier up a tier, climbing through x2, x3, x5 and on toward the feature's ceiling. The trail resets after each bump and starts filling the next tier. The part worth understanding is how those numbers combine. Wild multipliers on the same line are multiplicative, not additive, so three locked wilds carrying x2 each pay x8 across that line, not x6. The help text caps a single line at a 512x multiplier inside the feature. The whole round keeps going as long as a new wild or a new gem appears on a respin, and ends the moment a respin brings neither.

There is a smaller multiplier trick in the base game too. If exactly one wild is on screen and it helps form a four or five-of-a-kind, it can be handed a random multiplier of x5, x8, x64 or x512, which then applies to wins that include it, three-of-a-kinds on the same combination included. No free spins, no buy option, no jackpot tiers. The respin is the only gear-shift, and the 10,000x line at the top comes from chaining locked wilds while the gem trail keeps climbing.

The setting is a stone fortress throne hall, twin braziers throwing fire up the columns, a red carpet running to a pair of seated stone cats and an empty throne. The King and his Queen sit at the top of the paytable in metallic gold and royal purple, with a purple gem shield acting as the wild, and the usual A through 9 royals filling the low pays in cold blue and gold. If escalating respins are your thing, the same studio's Norse-flavoured Pillars of Asgard runs a different take on the locked-symbol idea.