Space Shelter: Alien Defense is a free-to-play strategic auto-battle game available on Android. Players are tasked with assembling a squad of space fighters to defend their shelter from relentless waves of alien invaders. With features like unit merging, rerolling for stronger allies, and trait upgrades, players can strategically enhance their team to survive increasingly difficult challenges. The game emphasizes tactical formation building and automatic combat, allowing players to focus on strategy while the battles unfold.

The gameplay involves merging identical units to unlock powerful fighters, making each battle dynamic and engaging. Players can choose traits that improve their squad's performance after each wave, adding a roguelite element to the experience. With a variety of units including mechs, gunners, and aircraft, players can create unique combinations to combat alien swarms and formidable bosses. The fast-paced nature of the game ensures it remains addictive and fun, appealing to fans of strategy and auto-combat genres.