Alien Syndrome (set 4, System 16B, unprotected)
ARCADE

Alien Syndrome (set 4, System 16B, unprotected)

Released in 1987 by Sega for its System 16B arcade hardware, Alien Syndrome is a beloved top-down run-and-gun shooter that defined 1980s arcade action. This specific version, the unprotected set 4 build, removes the original encryption locks that limited play on many retro emulators, delivering a smooth, authentic arcade experience without glitches or missing content. The game puts players in control of either Ricky or Mary, two space commandos tasked with infiltrating alien-infested space stations, research outposts, and alien planets to rescue trapped crew members before a countdown timer triggers a deadly explosion that wipes out the entire facility. Each level features sprawling, maze-like layouts teeming with over 20 different alien enemy types, from fast-moving facehugger-style parasites to giant, acid-spitting abominations. After rescuing the required number of crew members marked on your heads-up display, you gain access to the boss chamber, where you face off against enormous,

No download required
Save states supported
Works on mobile & desktop

The emulator loads after you press Start Game.

How to Play Alien Syndrome (set 4, System 16B, unprotected)

Move
WASD
ABAction
JK
XYShoulder
L;
STStart/Select
21

Save & Load States

  • F2Press F2 to save your current game state at any time.
  • F4Press F4 to load your last saved state.
  • F3Use F3 to switch between save slots.

Save states are stored locally in your browser. They persist across sessions but are cleared if you clear browser data.

Customize Controls

Click the gear icon on the emulator toolbar → "Controls" to remap keys.

Move
WASD
Action
JK|L;
System
2 Start1 Select
Save
F2SaveF4LoadF3Slot

Default layout for ARCADE. Remap in emulator settings.

About Alien Syndrome (set 4, System 16B, unprotected)

Alien Syndrome (set 4, System 16B, unprotected) is a classic ARCADE game you can play online for free in your browser. No download or installation is required — click "Play Now" to start instantly. Relive the experience of vintage console gaming with authentic gameplay, right in your browser on any device.

This title is part of the PLAYERETRO game collection, which features over 1000 classic titles across multiple systems. Use the keyboard controls shown above to move and interact. Save your progress with save states and enjoy Alien Syndrome (set 4, System 16B, unprotected) anytime, anywhere.

Play Alien Syndrome (set 4, System 16B, unprotected), the iconic 1987 Sega arcade run-and-gun shooter, for free online at PLAYERETRO. Fight alien hordes, rescue trapped crew, and defeat massive bosses

Game Guide

Mastering Alien Syndrome (set 4, System 16B, unprotected) is easy to learn but hard to perfect, so follow these tips to beat every level and defeat the final alien queen. First, prioritize picking up the map power-up as soon as you spawn into any level: the map marks the exact location of every trapped crew member, health pickups, weapon upgrades, and the exit door, saving you precious time wandering the maze before the countdown timer runs out. Second, match your weapon to the enemy type you’re facing: the default pea shooter is only effective against weak, small aliens, so swap to the flamethrower for tight corridors packed with swarms of minor enemies, the laser rifle for long-range attacks that pierce through multiple foes, and the rocket launcher for large, high-health enemy variants and mini-bosses. Third, save your limited-use smart bombs for two scenarios only: when you are completely surrounded by aliens with no escape route, or during boss fights to clear out summoned minions and deal massive damage to the boss’s core. Fourth, keep an eye on the required crew count displayed at the top of the screen at all times: you cannot enter the boss chamber until you rescue the full number of listed crew, so don’t head to the exit early, as you’ll just waste time backtracking. For co-op players, split roles to maximize efficiency: one player can focus on clearing a path and fighting enemies, while the other hunts for trapped crew and power-ups. Finally, learn each boss’s attack pattern: every boss has a predictable cycle of attacks, so observe for 10 to 15 seconds before engaging to find safe spots to stand and windows to attack, and always keep moving to avoid incoming projectile fire.