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.
Red Hot Spikes also make appearance in Bloons TD Battles Mobile. In Assault Mode they cost 1 per pile of 20 spikes for a max of five piles, but three Red Hot Spikes piles are provided for free in any Battle Arena.