Hades himself owns a beast; guard dog named Cerberus. And I am sure The Underworld contains many countless unusual beings.
hades
Yes... beasts, monsters, and the undead
A three headed hound named Cerberus.
Hades sent the worst monsters after Thalia as a way to undermine her and the prophecy surrounding her destiny. Thalia was a demigod with significant potential, and by targeting her, Hades aimed to disrupt the balance of power among the Olympian gods and their offspring. The monsters served to test her strength and resilience, reflecting Hades' desire to assert his influence and thwart the plans of the other gods. Ultimately, it was a strategic move to maintain his own dominance in the realm of the Underworld.
A dorky kid who turns out to be the powerful son of Hades
Hellhounds, Medusa, and Hades (technically, he is not a monster, he is a god)
The Titans? Like, Kronos (Zeus, Posiedon, and Hades dad)?
Zeus, Hades, and Poseidon, or the Big Three, swore on the River Styx, to no longer have demigod children, so when Zeus had Thalia, he broke his promise. Hades, angered that he broke his promise, sent horrible monsters after her.
There are many statues of Hades.
The Underworld, where Persephone is Queen, is the House of Hades - where the dead souls dwell, and where monsters abide.
Argolis and Elis had temples to Hades: there were many locations where Hades was worshiped.
Persephone, being Queen of the Underworld, dwells where Islands of the Blessed (where the heroes dwell after death) and Elysian paradise is - she also lives where such monsters as Cerberus guard the gates/house of Hades, and other monsters dwell.