How Did Hercules Kill Orthrus?

According to Apollodorus, Heracles killed Orthrus with his club, although in art Orthrus is sometimes depicted pierced by arrows.

How was Cerberus killed?

Cerberus kept many of the heroes in the old, epic stories confined to the underworld. ... Hercules descended into Hades, defeated Cerberus and returned without harming or killing the hellhound. Hercules managed to overpower Cerberus by grabbing him by the throat.

Who killed Echidna?

Although for Hesiod Echidna was immortal and ageless, according to Apollodorus Echidna continued to prey on the unfortunate "passers-by" until she was finally killed, while she slept, by Argus Panoptes, the hundred-eyed giant who served Hera.