O'Shamus McPherson is Jeff Fischer's magical leprechaun.
In "Joint Custody", Jeff attempts to give Stan a dowry of two ponchos and a magical flute that can summon O'Shamus for three wishes. When Stan attempts to haul Jeff to Florida to face drug charges after being set up by his dad, Henry Fischer, Jeff tries to escape by using the magical flute to call on O'Shamus but the black leprechaun is late in arriving. When he finally arrives after Jeff managed to hop on board a train to escape, he tells Roger to tell Jeff that summoning still counts as one of his wishes.
O'Shamus McPherson makes a cameo in "Widowmaker" when the cast and crew celebrate the 1000th vagina joke.
O'Shamus McPherson is voiced by J. Lee.