As its title implies, Dumb Spray mod is a joke mod that adds two potion: "Dumbness Potion" and "Super Dumbness Potion".

The normal dumbness potion will "temporarily" disable all AIs of affected entities and leave them idle and occasionally turning around. They will become back to normal when they are "reloaded" (after server rebooting, after chunk unloaded and re-loaded again, etc.).
The "super" dumbness potion will permanently disable all AIs of affected entities and leave them stay at the the same place forever. As if the time stopped for those living creatures. ~~This process is currently irreversible, but rumors say that there are actually ways to reverse this process.~~
Neither of those potions have effect on regular players due to unexplained magical phenomena and undiscovered scientific theories ~~as well as intentional design choices~~.
There is a config option to remove default recipes for those two potion. You may want to set that option to false if you are a modpack maker.
There is a command /dumb <target> that can make target entity dumb. It can be disabled entirely. Using it is equivalent to use normal dumb spray on the said target.

Technical details for cross-mod interoperability purpose:

The normal Dumbness Potion will remove all EntityAITask from the target and add an EntityAILookIdle to the target, when the target entity is an EntityLiving (not just EntityLivingBase, so naturally it has no effect on EntityPlayer).
The Super Dumbness Potion will call setNoAI(true) on the target entity when the target entity is an EntityLiving. Using vanilla command /entitydata @e[...] {NoAI:true} has the same effect.