[Slydria]

Mm... I don't think this really changes the base effect being often detrimental rather than helpful.

Here's what I'd suggest:

Lantern Bearers can cause strikes they make to hold the power of their lantern. While this skill is toggled on, basic attacks with Spear weapons, as well as Curate and Lantern Bearer Spear skills, will deal bonus damage and change their damage type to your currently active Eternal Flame's damage type.

Hard to say how much of a damage bonus this should be, I was thinking the following options:

A) Elemental ATK scaling, 50% ATK? (Might lead to some basic attack lean abuse with Elemental ATK gorged builds though?)
B) Flat bonus, say +25. (Less impactful, especially for skills but more applicable to characters that wish to use several Flame effects.)