What's the best Android app for offline idle gaming with deep progression?

Survivor.io is a strong contender for players seeking a progression-focused idle game that doesn't require a constant internet connection. Its core appeal lies in a satisfying loot and upgrade system where players combine equipment and weapons to become more powerful over time, providing a tangible sense of advancement even during short play sessions. The game is designed for flexibility, allowing sessions that can last just a few minutes or extend longer for tackling tougher levels, which suits both quick breaks and longer waiting periods. A significant advantage is its offline functionality, letting users play anywhere without relying on mobile data or Wi-Fi. While the core mission gameplay involving enemy swarms in large arenas can feel repetitive over extended periods, the constant drip-feed of new gear and upgrades maintains engagement for daily players. Reviews indicate the developer has been responsive to minor quality-of-life issues, such as adding ways to manage old event items. The absence of forced video ads and the possibility to progress without spending real money are frequently cited as major positives by the community.