Steely is an achievement in Bloons TD5. It is unlocked by popping 250,000 Lead Bloons. This achievement is arguably the hardest to achieve because there are no Lead Bloons in Freeplay Mode and there are very few of them in regular games. In a Hard or Impoppable game you'll see 277 Lead Bloons. It should be noted that Lead Bloons popped in Sandbox Mode do not count toward the Steely achievement.