Nitropolis 4 Slot Review

ELK Studios brought back their chaotic animal gang in February 2023 with Nitropolis 4, this time sending them out to an offshore oil rig to drill for nitro. If you're a fan of ELK's games, you'll immediately notice how much it has in common with Avalon Gold, especially the expanding grid and the "safety level" free spins.

As the fourth main game in a series that has grown pretty large, this one feels like a bit of a sideways step in terms of gameplay, and unfortunately, a slight step down when it comes to the math.

Nitropolis 3 had the exact same expanding board and massive 50,000x max win potential, but it offered a 95.00% RTP (Return to Player). In Nitropolis 4, ELK dropped that to 94.00%. It's a math profile you'll meet elsewhere at ELK: Cygnus 2 and Nitropolis 5 carry the same RTP and max win, and Cygnus 2 even prices its buys the same way. While the gameplay is still fun, as a regular player, it's always a bummer to see the RTP take a hit, even if it is just a 1% drop.

The base game is fine, but the free spins are where things take shape. Landing three or more bonus symbols gets you anywhere from 8 to 20 spins.

You start with a "safety level" of four rows. Every time you get a winning spin, the grid expands by one row (up to a max of eight), and the best part is that it doesn't reset on a losing spin. But what really makes or breaks your bonus round are the Nitro Reels (blocks holding multiple copies of a symbol) and the Nitro Multipliers. Once they land, they stick around for the rest of the feature.

Because those multipliers are sticky, even a dead spin can set you up for a big win. I saw it happen when I bought the standard bonus for 100x my bet. Half of my eight spins were completely dead, which was frustrating. But on one of those dead spins, a x10 multiplier dropped in. It just sat there waiting, and on the next spin, it turned a tiny four-of-a-kind win into a 39x payout. I ended up walking away with an 88x return, a slight loss, but it proved how quickly a dead bonus can turn around.

If one of your three or more bonus symbols is a "super" bonus symbol, which only ever lands inside a Nitro Reel, you trigger the Super Bonus instead. You can also buy straight into it via the X-iter menu, but it'll cost you a hefty 500x your bet (there are also cheaper X-iter options, from the 2x Bonus Hunt up to the 100x Bonus, though they all share that same 94% RTP).

You start with the maximum eight rows, and wins pay from both left and right.

I took a deep breath and bought the 500x Super Bonus just to see what it could do. I ended up getting 495x back, basically breaking even, but it showed me exactly how this game is designed to pay out. The base symbols are incredibly weak on their own. The real money comes when multipliers multiply each other. During my round, a x4 and an x8 multiplier lined up to create a global x32 multiplier. That combo turned a cheap, forgettable five-of-a-kind win into a 286x payout.

Nitropolis 4 is a fun, highly volatile ride. Once the board is fully expanded, you honestly stop paying attention to the symbols entirely. The whole game just becomes a waiting game, hoping those sticky multipliers find each other across the massive grid. It's a solid slot, provided you can look past the 94% RTP.