To dominate the leaderboards without cheating, focus your gold on these stats in order:

: Consistent players outpace "hackers" over time. Logging in daily for streak bonuses and completing every available daily mission is the most reliable way to stack premium currency for free. Essential Upgrades Hierarchy

: Reduces the window for enemies to reach your walls.

: Allows you to start dealing damage earlier, crucial for boss stages.

: In the early game, raw damage is often less effective than hitting more targets. Upgrading "Multishot" or "Attack Speed" allows you to manage crowds of enemies that would otherwise overwhelm a high-damage, slow-firing tower.