Make sure to read the commentary after you read the story...
The Phissel family originated in Germany, and were caught up in the religious wars that caused chaos in Europe during the 17th century. It is said that, at some point, the family became cursed because of their involvement in the religious wars. The family was forced to leave Germany, and moved to Ireland, but the women of the family died during the journey. The men established themselves in Ireland, and eventually re-married and produced a few new generations of Phissels. By the 19th century, the spelling of the family's name had changed to Phizzel, and they found themselves in the midst of the potato famine. What remained of the Phizzel family, one man, his wife, and his son and daughter, headed for the Americas. The curse struck again, and the wife and daughter died during transit.
Settling initially in New York, the Phizzel men eventually headed to Missouri, finding a home in Cape Girardeau. Eventually, the elder Phizzel died, and the younger Phizzel, Jeremy, maried and had two children of his own: a son and a daughter. The family moved into a house near the river (which some stories say that Jeremy Phizzel won in a card game during which he might have shot one of the other players dead).
One night, Jeremy's son ran from the house, terrified. He had just witnessed his father killing his sister and mother, and had barely escaped himself. Jeremy ran after his son, shouting "come and join your sister!" The son led Jeremy on a chase to the edge of the river, where, thinking quickly, the boy through a branch in, making it look as if he had jumped into the water. His father dove in afterwards, surfaceing a moment later, still shouting "come and join your sister!" The river's strong currents quickly overcame the man, though, and he began to sink. The last sound that the boy heard his father make was a gurgling noise as he drowned, that sounded something like the word "goblin."
The boy, scarred from this experience, began wandering the river banks, subsisting on whatever food he could find. Although generally reclusive, he would sometimes jump out at people walking by on the river and shout "Come oand join your sister! Goblin, Goblin" and thus became known as the Phizzel Goblin. Though he must have died long ago, his father having chased him to the river's edge over a century ago, people still claim to encounter his spirit on the riverbank.
Commentary: The Phizzel Goblin is an April Fools Day joke concocted by Gene Fitzpatrick and Bryan Minogue of the excellent Hometown Tales podcast. Absolutely nothing in the story above is true, it was written for the April 1, 2006 episode of the podcast. However, if you didn't look at the date that the episode dropped, there is nothing in the podcast that would tip you off immediately. The story is a bit sillier than normal, admittedly, but it makes use of tropes from well-known urban legends and ghost stories: a family that has been cursed (a'la Dudleytown), a child with developmental disabilities (in this case probably purely psychological in nature, due to emotional trauma) growing up without parents (similar to a story known as "The Retarded Farmer"), and a location where one is likely to see a creature that wishes to get you (similar to La Llarona). Although someone listening to the episode may think that Gene and Bryan are "winking" at the audience, and they may very well have been trying to, the show is similar enough to their usual episodes, in which they discuss actual urban legends, bits of local history, ghost stories, etc., that it's not at all clear that they aren't simply recounting an actual urban legend in their usual delightfully goofy style. Even a few things that should be tip-offs (such as the fact that, despite settling in an area and presumably producing several generations, there was always just on Phizzel nuclear family) are common enough to ghost stories and urban legends that they didn't stand out as cues that the story was a joke.
In other words, if you were going to try to design an urban legend, you wouldn't be able to do much better.
And so, if one types "Phizzel Goblin" into Google, you will find message boards, urban legend sites, and Q&A forums where people are trying to find more information about the Phizzel Goblin. Enough people figured out that it was a joke that there aren't too many people who believe otherwise, but there are still occasional people who go looking for more information on this "legend" of the Mississippi River. In other words, the Phizzel Goblin is the funny cousin of the Blair Witch.
Mr. Fitzpatrick, Mr. Minogue...well played, sirs.
Sources: Hometown Tales Podcast...and as evidence that some people bought it, look here, here, and here