As you’ll be buffing your Int and damage by stacking Rune Weapon, this will give you a nice buff to your converted damage.
It converts 63% at 6/6, you want to get +4 Rune at a min to get max ultimate level to convert nearly all (99%) your damage to Elemental. The Transmutation synergy converts % of Weapon Damage to Elemental. The Energy Drain synergy gives your attack 4% ADCtH, gives you an Energy Leech and reduces enemy OA and slows them. The extra damage is nice through but the skill requires a lot of points to max. You’re shouldn’t be getting hit so the retaliation doesn’t matter much. The Magical Charge synergy adds extra Elemental damage to your attacks and grants you Elemental Retaliation. Each stack boosts your Elemental damage, Total damage and Intelligence higher. The more stacks you have up, the more you get buffed. The more points you have in the skill, the more stacks you can get. Stacks decay over time when you are not attacking.