Aye, ye made it!! Welcome to the thread on Irish mythology. This will be a little bit odd, since the Irish didn't exactly have a pantheon, the Celts did. However, the Irish did have a butt-load of mythical creatures and spirits and legends, so I'll give you some!

According to Gaelic legend, the Merrow frolicked in the frigid waters near the rugged Irish coastline. These sea fairies were women from the waist up, and fish from the waist down. Although there were also male Merrow, they were far less attractive and irresistible than their female counterparts. They were believed to be monstrous, ugly beings with bright green hair who abducted and enslaved sailors. The male Merrow were so beastly that the females understandably preferred the company of human men. The females always wore enchanted caps which allowed them to swim far beneath the sea’s surface and to live safely underwater. According to the Gaelic myths, human men would see the beautiful female Merrow on the shores, and they would become smitten with them, despite the risks. Some would try to steal their cohuleen driuth (magic caps), so that they could not go back underwater. Many marriages (some less than ideal, given the method of “wooing”) were thusly arranged between Merrow and man. The Merrow who lived with men on the land (by choice or by necessity), would often tire of their new circumstances. In time, these charming creatures would grow homesick for the sea, and the lucky ones, who still had their magic caps, would find a way to return. Other female Merrow would sometimes lure desirable men with their sweet voices and their magical wiles, and then take them under the waves to live amongst their own fairy kind. They would dwell together in a bewitched state, sometimes for years and years.

The banshee is a female spirit  who heralds the death of a member of one of the prominent Gaelic families, usually by shrieking or keening. Legend has it that for great Gaelic families – the O'Gradys, the O'Neills, the Ó Longs, the McCnaimhíns, the O'Briens the Ó Conchobhairs, and the Caomhánachs – the lament would be sung by a fairy woman; having foresight, she would sing it when a family member died, even if the person had died far away and news of their death had not yet come, so that the wailing of the banshee was the first warning the household had of the death. In later versions, the banshee might appear before the death and warn the family by wailing.When several banshees appear at once, it indicates the death of someone great or holy. The tales sometimes recounted that the woman, though called a fairy, was a ghost, often of a specific murdered woman, or a mother who died in childbirth.

Known for the bad luck they purportedly dole out, the Far Darrig (or “Red Man”) is a kind of sentient humanoid Fae. Not usually particularly attractive or tall, they nonetheless interact with humans on a somewhat more regular (and surprisingly less harmful) manner than most other kinds of Fae. Far Darrig tend to pull quite terrible practical jokes, which tend to please only them, but can similarly give good luck to those who pass through such jokes unscathed and in good humour, or who offer them hospitality.

Far darrig have, on occasion, acted as the Fae who replace human children with Changelings, though this practice has largely ceased in the modern age, and it is more likely for a human to have a child by a far darrig, than to have one stolen and replaced with a Changeling. Far darrig are also more likely to be Lone or Solitary Fae than many others, for though they despise the presence of iron in the mundane world, they do much enjoy their practical jokes, to such a point that for many iron becomes irrelevant in comparison to their urge to prank.