Magical Phosphex

[beautyandnotthebeast]

After I discovered Phosphex from Warhammer 40k (basically a hyper corrosive, radioactive on steroids, toxic, liquid mist incendiary weapon that expands rapidly, can set fire to almost anything, is attracted to movement, burns underwater, can set water alight, has a sub zero burning temperature and the only sure way to stop is was exposure to a vacuum) and decided to create a magical version if it. But I'm not sure of how to pull all of it off.

How would you handle the super radioactive element? (It would need to be much more potent than the normal radiation enhancement and the radiation would need to last much longer).
How would you handle an moving area attack that grows larger instead of just moving?
How exactly would you handle the attracted to movement? (Vibration Sense seems like the closest to it, but it can detect things that aren't moving).
How would you handle the setting water alight part, and making sure that being underwater doesn't reduce range like the Underwater enhancement does?
How would you ensure that a vacuum is able to stop it?
And does the sub zero flames affect the Innate Attack, or is icy fire still treated like normal fire?