Look Out! Some Lead Bloons are on their way. If you don't have anything that can pop them, never fear! Just drop a stack or two of Red Hot Spikes on the track. Each stack pops up to 20 Bloons. Costs 5.
~ When Lead Bloons first appear (before a rush).
... Use Red Hot Spikes with Lead Bloons or other nasties that slip through your defenses.
~ Part of a quote after starting a track from My Tracks
Red Hot Spikes are a special variant of Road Spikes that were added to Bloons Monkey City, along with the Monkey Boost, in the 4th Feb 2014 update. Each stack costs 5 and can pop 20 Bloons, and ten can be used for each tile or attack (mobile) when received as a bounty. In addition, Red Hot Spikes can pop Lead Bloons. Fortunately, they last until the tile or attack ends.