His feast day was originally given as 9 February, although this had moved to the 10th or 12th by the 16th century[1] and is no longer observed by either the Anglican[4] or Catholic church in Wales.

[1][10][11] He was credited with granting his brother Seiriol the land for his monastery (Welsh: clas) at Penmon on Anglesey[1] and, later, his hermitage on Puffin Island.

[12] He also lured the Breton saint Cadfan from Tywyn to found St Mary's Abbey, the first religious establishment on Bardsey Island.

[1] The present church there, which was erected in the late 15th or early 16th century,[2] had a gilt and crowned statue of him prior to the Reformation[14] and bears Latin inscriptions reading Æniani Rex Wallie and Rex Walliæ ("Einion, king of Wales").

Miraculous locations nearby include Ffynnon Engan ("Einion's Well") and Ol Troed March Engan ("The Hoofprint of Einion's Horse"), a petrosomatoglyph near Castell Cinan whose collected rainwater was claimed to possess curative powers.