Fisher King Slot by Endorphina

Five broken hearts sit under the reels, one beneath each, and the whole game points toward filling them. They only matter in the free games, which start when three or more scatters land (three, four or five scatters open 10, 15 or 20 spins respectively, and the round retriggers). Once you're in, a Holy Grail symbol can drop on any reel, and when it does it feeds lifeblood into the heart below. Two grail landings fill one heart completely. The payout isn't per heart over the whole round, though - it's how many hearts you complete in the same spin. One filled heart pays 3x your bet, two pays 10x, three jumps to 50x, four to 500x, and filling all five in a single spin is the top hit at 2000x. So the round is a balancing act: you want grails spread across reels rather than doubling up on one, because simultaneous fills are where the money is.

The clever bit is what happens between rounds. A heart that's only half full doesn't reset. Its progress carries into your next free games series, as long as you keep the same bet and the same number of active lines, so a round that ended one grail short of a payout isn't wasted. The wild already substitutes for everything except the scatter in the base game, and during free games it lands stacked, filling reels and stretching line wins while you chase grails on top.

If you'd rather not grind out scatters, the Bonus Pop button buys a package of 10, 15 or 20 free games outright. Anything won through Bonus Pop can't be sent to the gamble, which is worth knowing before you buy in. That gamble is a card guessing game - beat the dealer's card to double, repeatable up to ten times, with a joker that beats everything. Running quietly underneath it all are three networked mystery jackpots (Grand, Major and Minor) that drop at random with no input from you, weighted toward higher bets. Those are network progressives, separate from the heart prizes.

The setting is straight Arthurian legend. The reels sit in a heavy gold frame against a midnight-blue board inside a candlelit stone hall, treasure glinting in the dark behind them. The premium symbols are hand-painted - the bearded, crowned Fisher King and a red-haired maiden, alongside a young knight - with jewelled coloured royals (10 through Ace) filling the lower pays. Deep blue, gold and amber throughout, solemn rather than flashy, which fits a game built around a Grail quest.