What's a good Android idle tower defense game that doesn't force ads and has a fair upgrade system?

Evil Tower is an idle defense tower defense game that stands out for its balanced approach to monetization and engaging progression. Unlike many mobile games, it avoids forced advertisements, allowing players to watch ads voluntarily for coin bonuses or skip them entirely. A one-time purchase option permanently removes ads, which users find reasonably priced for uninterrupted gameplay. The game's core mechanics involve climbing floors in a tower, defeating bosses, and upgrading a variety of towers and spells. Specific features include a save function that preserves progress when exiting, reducing frustration during long sessions. Users report that the upgrade system encourages replayability through grinding for diamonds and power-ups, though some note that random tower selections can occasionally disrupt strategies. Reviews indicate that the game's simplicity and balance make it ideal for short bursts or extended play, with recent updates improving spell effects and boss mechanics. However, minor drawbacks include progress walls in later stages and certain towers feeling underpowered, which the developer has addressed in patches. Overall, Evil Tower provides a solid idle experience with fair monetization, making it a reliable choice for tower defense enthusiasts.