Boom! Slot by Playtech

Most hold-and-win rounds lock you to a fixed grid. This one blows the roof off. The BOOM! Hold & Respin starts when the glowing green and blue cash bombs land and stick, each holding a value worth anywhere from 1x up to 100x your bet. You get three respins, and every new bomb resets the count. The real twist is the height. Every two bombs that land alongside a Tool symbol unlock a fresh row, so the three-row board pushes upward, one tier at a time, as high as nine rows.

Then the height itself starts paying. Any held bomb sitting on the seventh row gets doubled, bombs on the eighth row are multiplied by five, and any bomb that climbs all the way to the ninth row turns into a Star, which collects the values of every bomb on the board. So the bombs you want are the ones riding highest. Everything banks once the respins run out. Four fixed jackpots live in this round too, from the Mini at 20x up to the Grand at 2,000x your bet, and they drop at random while the grid is still expanding.

Outside that, the base game is a plain fifty-line board where the purple starburst Wild stands in for everything except the bonus and cash bombs, and pays on its own. Three or more of the gold B.O.N.U.S. bombs open eight free games, and the hook there is reel three, which turns into a special strip stacked with nothing but Wilds and more bomb symbols, loading the middle column with substitutes every spin. No buy button and no ante bet, so both the free games and the Hold & Respin have to show up on their own.

The whole thing is dressed like a neon game-show set, the reels floating on a wall of glowing blue diamonds beneath Grand, Major, Minor and Mini jackpot ribbons, with a comic-book BOOM starburst flaring off to the side. The pyro-technician theme shows up in the symbols: stone-carved silver royals, wobbly green paint-balloon figures, tangled bundles of colored fuse wire and paint-splattered safety goggles, all in electric blue, magenta and gold.