There are four hidden retro stages in Streets of Rage 4 that are among the most well-concealed secrets in the game. There's an arcade cabinet in four of the game's 12 stages that conceals a portal back to the 16-bit era, but if you didn't know any better, you'd think they were just a background gag.

Here's how to find and enter each retro stage.

How to Find the Throwback Fights in Streets of Rage 4

If you've played through the game on any difficulty, you've likely spotted the Bare Knuckle arcade machines in the background of four of the levels. Each can be destroyed and can contain items.

At first, they look like a piece of set dressing that's also a decent in-joke, as Streets of Rage shipped in Japan under the name Bare Knuckle. Each one of the arcade cabinets is a little more significant than that, however, as they're hiding four secret boss fights.

To access them, you need to hit the arcade machine with a stun gun. No other weapon will do. These are often carried by nearby enemies whenever there's an arcade machine around, although if you use up or ditch the stun gun beforehand, you're just out of luck. You'll want to avoid picking them up at all, as a stun gun in a player's hands breaks after one hit.

When you destroy the arcade machine with a stun gun, your characters are instantly transported to a boss room from a past Streets of Rage game, to face an old 16-bit boss, just like the ones you might have faced in the old Genesis version. You have one life in which to beat this guy; if you lose, you're punted back out into the level. You don't actually lose the life, however, and you do get thrown back outside at full health, so on higher difficulties, you might get some survival mileage out of entering the retro stage and deliberately throwing the fight.

If you win against the retro boss, however, you receive an extra Star Move token for use later in the level.

The first time you enter a retro boss fight, you receive the Throwback Trophy/achievement. That, the Star Move, the points you get for fighting the boss, and the sheer cool factor are your only real rewards here.

Strictly in terms of cost/benefit, it's worth doing a retro boss fight if you're farming points for character unlocks or just trying to break your own high score. This is particularly useful considering the existence of the Bloody Knuckles Trophy/achievement, which challenges you to get a lifetime score of 5,000,000.

Where to find the retro bosses, and what to watch out for along the way, is listed below. If you'd rather be pleasantly surprised, stop here to avoid mild spoilers.

Stage 2: Precinct

There are a ton of cops with stun guns throughout this level, so having one with which to activate the arcade machine shouldn't be a problem. They only last for one hit before they break, though, so don't use them all up.

Look for the arcade machine in the background right before the open jail doors, on the left side of the small room in the back. Give the machine a jolt to travel back to Streets of Rage 2 and fight Jack. You can actually bring one of his knives back out into the main game with you, although it breaks easily.

Stage 4: Old Pier

The arcade machine is readily visible in an arcade you pass near the end of the level, under a helpful neon sign, but it doesn't initially look like you can get inside. There's an open doorway to the right of the arcade that will let you enter, however.

Zap the machine to fight Zamza, the claw-wielding psychopath from Streets of Rage 2. He's fast and has a lot of invincible moves, so he's tough to bring down in one life.

Stage 6: Underground

You have to be careful here to avoid accidentally destroying the arcade machine. It's set up near the end of the pool hall, with a thug playing it as you approach, but it's really easy to put a thrown weapon or flying enemy through the cabinet before you can use it. The stun gun you need is hidden beneath a nearby table.

When you activate the retro fight, you'll head back to level 5 of the original Streets of Rage to face the pro wrestler Abadede.

Stage 8: Art Gallery

Once again, the Bare Knuckle cabinet is right out in the open, in the storage area behind the main gallery, so you have to be careful or it'll become collateral damage. There doesn't initially seem to be a stun gun lying around to activate it with, but there's one hidden behind the junk in the foreground in front of the arcade cabinet.

When you activate this cabinet, you'll get the chance to take on Mr. X, the final boss of Streets of Rage 2, and his bodyguard Shiva. This is a difficult two-stage fight, particularly on only one life, where you need to take Sheva on before Mr. X will fight you. Good luck.

SoR4 came out today to impressive reviews. We're still digging into it, but in the meantime, check out some of our other stories from today:

With Streets of Rage finally out of retirement after 24 years, we're curious what other long-dormant '90s Sega franchises could use a revival like this. We're holding out for Kid Chameleon, but feel free to share your favorite inexplicably-dead Sega series with us on Twitter, @PrimaGames.