Full Potential

---

Win a chapter 4 (or later) mission with level 3 towers only and no selling.

---

This achievement requires that you win any Chapter 4 or later mission with only level 3 towers on the map at the end of the game, and without having sold any towers along the way. While most of the maps can be won this way, the easiest approach is likely to play Chapter 19 in Grinder mode on easy and play only Gun towers. After you reach wave 10 and have a stable path, upgrade all of your towers to level 3. From that point on, don't place any towers unless you have 700 resources available, and immediately upgrade them to level 3. Note that you do not need to get a gold (or any) medal to unlock the achievement, you merely need to finish the game with at least one core still on the map.