Cave of Gems Dice Slot by BF Games

Each reel here has its own counter sitting on a copper plaque above it, and three Nitro potion bottles in the right places will tip that reel into a Persistent Wild for the next three spins. Every position on the reel turns into a Wild for the duration. Single, double and triple Nitro bottles add 1, 2 or 3 to whichever counter they land above, and the moment a fresh reel locks in as Persistent, every other active Persistent Wild reel has its three-spin clock reset back to full. So a well-timed second trigger can keep an entire wild column alive long after it should have expired.

Push it all the way and you get the Full House. All five reels Persistent at once pays a flat 200x the bet, no line wins counted, and every counter wipes back to zero. That's one of two fixed credit prizes built into the game. The other is the Grand Reward at 500x, but it only fires inside Free Games.

Free Games swap the per-reel counters for a single Grand Nitro Meter. Three Treasure Chest scatters award 10 spins, four give 15, five hand out 20, and retriggers from 2/3/4/5 chests stack +5/+10/+15/+20 on top. Nitro bottles now feed the Grand Meter directly, and at 15 it pays the 500x and resets. Persistent Wild reels still carry over from the base game into the bonus, but not the other way around, and crucially not when you buy in. Any reels you parked at counter level 2 in base play vanish if you pay for spins instead.

The Explode Feature is the volatility lever. Random trigger during Free Games, but only when the Grand Nitro Meter is sitting at 3 or higher. It scatters Bomb Wilds across random reel positions equal to whatever the meter shows, then resets the meter to zero. Bomb Wilds substitute for line-paying symbols only, so they fatten paytable hits without contributing to another Persistent trigger.

The Buy Feature is rare for BF Games and offers three tiers: 50x for 10 spins, 90x for 15, 130x for 20. The 130x option lines up cleanly with the 500x Grand ceiling if the Explode lands well, which is the whole reason to pay top tier.

Visually it's a goblin's underground gem-mining workshop. Paper lanterns in blue, orange, green and red hang from rope across the cave roof, a turquoise gem ridge glows behind the reels, and the goblin himself stands to one side of the grid in mining goggles and a leather apron, his cart full of glittering stones parked next to him. Symbols are the Belgian-market Dice cut, so the royals carry pip overlays instead of plain letters, and the high-pays are the cart, the chest and gem clusters. Counter plaques sit right on the cabinet above each reel, which makes the Nitro state legible at a glance, a small but smart UI choice for a mechanic that lives or dies on the player tracking three numbers at once.