His temper, and his moodiness.
Yes when he is mad
Because he was a god of the dead.
God of the Underworld.
If you angered him. He would place you in Tarturus.
he could choose where you went after you died
He made Hades a helmet that could make him invisible.
Yes, if he doesn't like you, I mean he's the lord of the dead.
The Greeks didn't make Hades. Hades' parents the Titans Kronus and Rhea made Hades.
The cyclopes made hades his helm of darkness.
The Cyclopes made Hades his Black Crown Of Invisibility
All the gods of ancient Greece could be considered dangerous, especially if they were upset or offended in some way. For the most part, though, Hades kept to the Underworld (also referred to as Hades) and left the living alone. The most notable exception was when he stole Persephone to be his wife. He was more inclined to answer curses than prayers so he could be considered dangerous in that sense. The people of Ancient Greece rarely even said his name, although this was likely more from fear of his station than fear of his specific wrath. More than most gods, though, Hades was reguarded as just and fair.
Hades has not been known to cause earthquakes; however, Poseidon has.