Underworld Idle is designed as a long-term idle game. Progress may seem slow, but consistent check-ins and strategic decision-making can lead to satisfying advancement over time without the need for microtransactions.

There are several tips for maximizing progress in Underworld Idle without spending money:

1. Focus on maximizing prestige points. This is one of the most effective ways to make progress in the game.
2. Check in once or twice a day. The game is designed to reward periodic check-ins rather than constant active play. Many players find that checking in 1-2 times daily is optimal for progression without spending money.
3. Take advantage of the in-game clock mechanic. This feature rewards players with tokens, upgrades, and resources daily, helping you progress even when not actively playing.
4. Plan your rebirths carefully. Each rebirth should feel meaningful and be part of a larger strategy to reach your next milestone.
5. Be strategic with upgrades. Carefully consider which upgrades to purchase, as some may slow down your progress if obtained too early.
6. Utilize the offline earnings mechanic. While the game doesn't have full offline progression, it does offer some offline earnings for certain resources.
7. Manage your energy use efficiently. The game has an energy system that allows you to allocate resources strategically.
8. Be patient. The game is designed to be slow-paced, so progress without spending money will take time. Many players find this pace enjoyable as it allows for a more relaxed gameplay experience.