Note: As of today, the Mr. X Nightmare DLC is unavailable for purchase on Switch, due to a technical issue that does not impact review codes. Publisher Dotemu is working to remedy the issue.

Last year's Streets of Rage 4 is required playing for anyone remotely interested in beat-em-up games. It channels the spirit of the original trilogy, infuses the visceral action with thoughtful new mechanics, and boasts some spectacular art and music. Now, roughly one year later, it's even more attractive, thanks in part to a free update and in part to paid DLC in the form of Mr. X Nightmare, which adds three new playable characters and an endless rogue-like survival mode. Is it, like the base Streets of Rage 4 experience, indispensable? No, but it does make an already great game even better.

The premise of Mr. X Nightmare is simple: after saving Wood Oak City once again from evildoers, the heroes of Streets of Rage realized that they should prepare themselves for the next villainous scheme. So, they contacted the cyborg Dr. Zan, who built a simulation machine from the remains for Mr. X's brain that would recreate every permutation of enemy encounter they might face. 

The result is the game's new Survival mode, an infinite succession of randomly-generated levels packed with RNG weapons, perks, and baddies. It's a meaty mode with near-endless replay value, even if it feels repetitive and grindy at times.

Here's how it works. From the main menu you'll choose Survival, then select either a totally random simulation or the weekly special sim, a set sequence of levels, enemies, and perks. From there you'll choose your character, invite any local or online guests, and enter the nightmare. Each simulation unfolds in a similar way. You enter a closed arena, beat up any and all bad guys, and clear the level. The game will then present 2-3 perks for you. These might add a flame modifier to your charge attack, spawn a helper at the start of each successive stage, increase your attack power when under 50% health, etc. Then it's on to the next stage to complete the cycle again. You have only a single life; when it's gone the simulation ends and the game records your high score.

Thanks to its random nature and rogue-like perk system, each run feels a little different, granting the game nigh infinite replay value. It's also a great excuse to revisit the stellar mechanics and interesting characters of the base game.

Last but not least, playing through Survival will ultimately unlock several items, including weapon packs, concept art and, most importantly, alternative moves for all the main playable characters. This last bit might not sound like much, but the inclusion of alternative moves has a meaningful effect on how you approach Streets of Rage 4, since they can be used in any game mode.

That's the good news. The not-so-good news is that unlocking all those alternative maneuvers will take some time, and plenty of grinding. You must brave the gauntlet several times per character to get every last variation. Is it a slog? Not exactly, but with only so many backdrops and situations, the action can turn repetitive, even after only a handful of runs. Furthermore, a bad sequence of perks or a super strong enemy early on might cut your random run short prematurely. Indeed, the randomness of Mr. X Nightmare — its calling card and the reason for its obscene replay value — can, at times, be a liability. The action, controls, and mechanics are still as great as ever, but random rooms packed with bad guys simply can't compete with the bespoke brilliance of the base campaign in Streets of Rage 4.

Luckily, Survival mode is only part of the Mr. X Nightmare DLC equation. The other part introduces three (well, four) new playable characters, available across all modes. They are fan-favorites Estel Aguirre, Max Thunder, and Shiva, who previously appeared in Streets of Rage 4 as bosses. As you'd expect from Lizardcube, Guard Crush, and Dotemu, all of whom contributed to the development of the game, the new characters are fleshed-out, interesting, and mechanically diverse.

Estel, a tall, muscular special forces officer, is a balanced fighter especially good with wallbounce combos. And her blitz attacks are great at covering horizontal distances quickly. Overall, she's probably the least interesting, mechanically, of the trio, but still a welcome addition to the roster.

Max Thunder, a professional wrestler who debuted in Streets of Rage 2, is more intriguing; he's one of the slowest and strongest characters, and he can jump while grabbing an enemy. He's particularly good at crowd control.

The best DLC character, though, has to be Shiva. A fast-moving martial artist, Shiva lights up the battlefield. His forward special move, Senretsu Ken, adapts to the distance of the enemy, and his air combos are peerless. Indeed, Shiva has two air special moves. The only downside is that Shiva cannot handle weapons; if he tries to pick one up he'll flip it forward.

Mr. X Nightmare also includes a secret fourth playable character, which you'll have to discover on your own. If you want a hint as to who it is, check out the unlockable survival artwork pack 2.

This is a Streets of Rage 4 expansion, so you can expect the best of the best when it comes to art and music. The new characters and backdrops look great, and all the alternative move animations blend in seamlessly. On the music front, Dotemu brought in composer Tee Lopes to score the DLC. Lopes, who previously worked on Sonic Mania and League of Legends, delivers some great tunes, including but not limited to "A.I. Supply" and "Spotlight Summersault".

One quick note on the free Streets of Rage 4 update. While it launched simultaneously with the DLC, it's separate and entirely free. It includes a remarkably deep training mode (which more than anything proves Streets of Rage 4 has more in common with a 1v1 fighter than your average beat-em-up), color palette options, a devilish New Mania+ difficulty, and a host of balancing tweaks. 

Streets of Rage 4 was already great. Looking back, it's one of the finest games of 2020 and arguably the pinnacle of the Streets of Rage series. Now, thanks to the Mr. X Nightmare DLC, it's even greater. The three new characters — Estel, Max, and Shiva — enhance an already stacked roster, and the endless Survival mode adds considerable longevity to the core experience, as long as you don't mind the repetitive, grindy gameplay loop. If you're looking for an excuse to revisit Wood Oak City, this is it. Moreover, at $8, it's a steal.