Thread:84.198.59.120/@comment-4669534-20120424035651

Phenomenon is singular, as in a single occurrence. Phenomena is the plural form, meaning there would be multiple occurrences, which is technically appropriate in this case. It's a weird Latin-adopted word, just like data (singular: "datum"), but good looking out. Nice catch that somebody copied it from Bulbapedia too, by the way :3 