Bud and Lou are two pet spotted hyenas belonging to Harley Quinn.
One of them could be seen inside Harley's mind in the episode "Being Harley Quinn" although it's unknown which one of them. They made their first full appearance in the season 2 premiere "New Gotham" in which they are seen pulling on Harley Quinn's sleigh in the opening scene. Once she arrives at their hideout she gives them both a steak. They were seen again in "Trapped" being fed bone-shaped biscuits by Doctor Psycho.