Alright then. Proposal: The Igylliones were Uralic-speaking charcoal-burners, seen by their neighbors as vermin (living on meadows?), and they disappeared at some time after Ptolemy mentioned them.
****GK: With Ptolemy, problems of orthography and localization abound (Gudmund Schutte has pointed out a great many). So far I worked on the assumption that the Igylliones (Igulliones, Igolliones)--Kostoboki--Transmontani "up to the Peuce mountains" sequence was an -->east/southeast sequence like that of the Venedae--Galindae-- Sudini-- Stavani-- Alani (unfortunately I don't have access to the maps themselves). But what if it's more of a north/south sequence? Also, a sequence that is actually northeast of the major "border" ("above Dacia") sequence Bastarnae--Carpiani--Peucini (which Schutte would likely reduce to simply Bastarnae--Carpiani, since he considers "Peucini" to be a "doublet" (cf. Tacitus). And there is the further complication that the ethnonym"Kostoboki" may have been repeated, the Tyras being the boundary of Prolemy's "Dacia" and "Sarmatia", and the Kostoboki occupying both banks of the river, thus
being at the same time in Dacia and in Sarmatia...
On this alteranate scenario the Igy(gu,go)lliones would not have been Bastarnae. As between the Stavani and Kostoboki, they might fit the new "Late Zarubinian" culture which emerged on the southern Boh(g) river after the catastrophic end of classical Zarubinia in Farzoi's time, and which was a mixed affair, Zarubinian traditions coexisting with incoming Przeworsk elements and northern infiltrations from the area of the Belorusan Shaded Ware culture (about a 60:20:20 split in discovered sites). Perhaps Pachkova's study will help to clarify things. Whoever these Igylliones were, (and vassals of the Aorsan/Alani to boot) they were pushed northward by the Goths, and eventually fused with the early Slavic Kyivan culture.
Don't know about the language, but there was nothing Uralic about the material culture. Nor BTW along the Vistula where Ptolemy located his "Finni".*****