Blade Maelstrom is the final upgrade on the second path of the Tack Shooter. It is unlocked upon reaching Rank 20. It is the special ability for the Tack Shooter in BTD5, BTD Battles and BMC. When activated, the Blade Maelstrom rapidly shoots two streams of blades, which spiral outwards. It costs $2295 on Easy, $2700 on Medium and $2915, Hard and $3240 on Impoppable. Its ability cooldown only lasts for 20 seconds.
Despite the description stating it is "unstoppable," Blade Maelstrom will be stopped by Lead Bloons. This can be prevented by a 0/3 Monkey Village.
Each of the blades have unlimited pierce, making it good for thick groups of bloons (Helpful if Regen Farming gets out of control and it's cheaper than Ground Zero). However, you may need 2 or 3 to destroy all Regenerating Bloons. Several of them can destroy a whole map of regenerating Ceramic Bloons.
When the ability is activated during the time the rings show up the game is very likely to lag a bit, however nothing happens to the gameplay.
It will only do a little damage to the bloons if put far away from them.