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O'Riley's Pub has long been in conflict with the pub across the road, O'Neill's Bar and Grill. The feud has become particularly nasty in recent months, with the owners regularly clashing in the middle of the street. The thing is, Mr O'Riley poached the star French chef Francois Cheval from the O'Neill's kitchen staff in the summer, and relations have only gone downhill from there...
So the horse is part of Mr O'Neill's revenge plan, inspired by his love of Ancient Greece and the tale of the Torjan Horse. He attached a hidden camera and microphone to the saddle and 'accidently' led the poor horse through the door of O'Riley's at some point during the new year celebrations, hoping to catch some illegal activities on camera that could shut down the rival pub for good!
The horse is called Brian and actually belongs to O'Riley's regular Quinn 'The Pint' McKenna. He inherited it from his beloved grandma and it lives with him in his one-bedroom apartment in downtown Smeet City. Needless to say, it's not the most hygenic of living situations, although there is some debate amongst the locals as to whether the smell is more to do with Quinn himself than Brian the horse. As with most nights, Quinn came to O'Riley's to celebrate new year and to enjoy a few jars of his favorite beer, Smeetville Trinity Pale Ale. What a hipster.
Anyway, it turns out old Brian is pretty terrified of fireworks, something Quinn's 8 year-old nephew once discovered at great cost when he let off a firecracker in Quinn's kitchen (the child hasn't been back to visit his uncle since and still sees an animal shrink once a week). So Quinn had to take Brian along to O'Riley's, which was fine until Quinn passed out under the bar and left Brian all on his lonesome... :(