All offensive potions strip Fortified property off of Lead and Ceramic Bloons, and greatly damages MOAB-Class Bloons.
~ BTD6 Description
Perishing Potions is the 2nd upgrade for the 2nd upgrade path for the Alchemist. With this upgrade, the Alchemist's potions remove the Fortified property from Lead and Ceramic Bloons as the description states. Potions deal 5 damage per hit to MOAB-Class Bloons and 20 damage to Fortified MOAB-class Bloons. It costs $405 on Easy, $475 on Medium, $515 on Hard, and $570 on Impoppable.
Being one of the few upgrades that deals extra damage to Fortified MOAB-class, Perishing Potions is a rather cheap upgrade for destroying the Fortified MOAB on Round 40 ABR, and is by far one of the few upgrades that are good at destroying the Fortified MOAB.
It can ocassionally can be used as a supportive DPS tower in later game when Fortified blimps and ceramics run rampant.
Besides defortification attacks such as by Mortar Monkey's Shattering Shells upgrade, Perishing Potions is the only upgrade that deals greater than 2x damage to Fortified MOAB-class than on non-Fortified MOAB-class. (Spiked Balls and Heavy Shells both deal only +1 damage to Fortified, dealing 2x damage and 1.5x to Fortified MOAB-class compared to normal MOAB-class, respectively)