Great Blue Slot by Playtech

Two oyster scatters is all it takes to open the free games, a low bar for a slot this old and this volatile. Land them and a pick round runs before a single free spin turns. You tap to reveal how many spins you have won and a win multiplier that then applies to the whole bonus, up to 15x on everything you hit. Five oysters can stretch the round toward 33 spins, so both numbers, the spin count and the multiplier, are settled and locked before the reels move again.

The grey orca is the wild, and it carries both modes. It stands in for every symbol except the oyster, it lands in full stacks that can bury a whole reel, and it is the top-paying symbol in its own right, so a column of whales scores as a line win rather than just plugging gaps. In the free games those stacked whales also carry the bonus multiplier, which is where the round finds its bigger hits.

The reels sit in a calm stretch of deep-blue sea, sunlight cutting down through bubbling turquoise water over dark coral shadows. The creatures are painted rather than cartooned. The orca and a grey great white top the paytable alongside a green sea turtle, an orange seahorse, a yellow butterflyfish and a pink starfish, above the usual glassy blue card royals. The pink pearl oyster is the only symbol that pays from anywhere, and it pays on its own before it ever counts toward a trigger.

There is no buy feature and nothing to ante up. This is a 2013 title, so it all rests on that one pick-em free-spins round and the stacked whale, with none of the side mechanics newer slots pile on. A separate Great Blue Jackpot version bolts progressive prizes onto the same reels. This is the original, running on the base math.