The boiling point of mercury is 357 degrees Celcius. Mercurius can stand very high temperatures. His mercury blood can stand these temperatures without killing him. This makes him able to go into hot buildings and save people.
Mercury is extremely toxic, in which is a good thing to have to be a super hero. Mercurius has a hole in his wrist that can shoot mercury blood out. He shoots this at people and if they breath in the vapor or it gets onto their skin they could die. This could stop robbers from robbing.
Mercurius later meets an enemy that he needs to save everyone from. The enemy can free any substance in 10 seconds. This is a weakness to mercurius because if his mercury blood freezes then it won't be able to shoot liquid mercury at people. This a physical property.