Note that Luden's Echo does not affect the classification of the triggering ability - an ability that applies spell damage will apply spell effects from that damage classification, and not Luden's Echo's.
Luden's Echo will not apply champion-specific spell effects, such as Blaze, nor duplicate the effects of a champion ability (e.g. Blinding Dart will not blind all enemies hit and Baleful Strike will not generate ability power for every enemy killed or enemy champion hit).
For large area of effect abilities, Luden's Echo will pick a main target based on the pick order.
This item was designed to replace the removed Deathfire Grasp as the third high-end AP item.
The name "Luden's Echo" was data-mined from the PBE update pushed on 2015-02-17. The item was later enabled for testing with placeholder name "Item 3285".
The name "Luden's Echo" comes from a player who reached 1000 referrals on the old Refer-A-Friend system.
During testing on the PBE, the item's icon was a purple recolor of Statikk Shiv.