Renting

Renting is a new feature in BTD6. It allows you to rent upgrades that are locked for 10 minutes. It costs 1/3 of what the thing costs, rounded up. The 10 minutes only tick during rounds. When time is up, your towers get downgraded. You can only rent 1 upgrade per tower at a time, and you cannot rent 4th or 5th tier upgrades. (Because you could get a TOTMG for $33,334)