YouTD

The main conflict I feel with this tower is it's intended use. A spell damage aura is to buff spell damage towers. An aura that converts attack damage to spell damage is either for a hybrid or an attack damage tower. Hybrid towers already benefit from both attack and spell damage auras, so it doesn't feel necessary for this tower to exist.

That being said, having redundant spell damage auras spread across multiple elements is healthy for the game so people are not forced into certain elements to play certain strategies and are rewarded for collecting all of them in a single run. In general tower diversity is a benefit to the game to increase skill expression through strategy and adaptability.

This tower is providing 15+15% (30) spell damage, compared to Red Ball Lightning (when upgraded) giving 35+15% (50), meaning the 5-10% attack damage conversion to spell damage is it's main "unique" effect. Arguably the spell damage it provides is balanced around boosting the attack damage it converts (so it's like 13% attack damage as spell damage once all bonuses from this tower are accounted for). What I'm saying is in terms of balance the tower doesn't concern me.

Aura towers are also notoriously hard to have suggestions for. It just feels like another thing I would build near my carry/ies but not put much thought into.

This totem (and windfury totem) are heavily inspired by their respective World of Warcraft totem effects, deliberately have effects of both the vanilla and Wrath of the Lich King iterations.

Before Wrath, Flametongue Totem would add fire damage to players attacks. This was originally going to be Elemental damage. Which would've made you go, oh cool extra damage with potential armor interactions (in cases where your main attack was a different damage type).
After Wrath, Flametongue Totem instead granted increased spell damage.

Problem with % attack damage as extra Elemental damage is it doesn't synergize with the spell damage boost (unlike Windfury Totem where the attack speed works in tandem with the trigger), so it was changed to % attack damage as extra spell damage. The armor interaction of % of damage as extra bla bla is still there, but now its just spell damage so the interactions are different.

It wasn't created for hybrid carries, it's just meant to be a unique damage boost aura.