Card Trivia:Old Entity Hastorr
- This card's name and art is a reference to Hastur, a fictional deity from the works of American horror writer H. P. Lovecraft (though he was actually created by Ambrose Bierce, in whose works Hastur originated as a benevolent deity of shepherds). August Derleth developed Hastur into a Great Old One, along with describing The King in Yellow as one of Hastur's avatars, in which form Hastur appears in the artwork of this card.
- The larger shadowy monster in the artwork of this card may be a reference to The Feaster from Afar; another avatar of Hastur depicted as a black, shriveled, flying monstrosity with tentacles tipped with razor-sharp talons that can pierce a victim's skull and siphon out the brain.
- This card has the highest ATK among Level 4 Synchro Monsters, tied with "The Fabled Unicore".
- This card's last effect may be a reference to the debilitating insanity with which many who encounter the creatures from Lovecraft's work are subsequently afflicted.
