Missing Info

It would appear you didn't read the article on magic fusion which clearly states that fused magic has a damage equal to spell A + Spell B as its base (unless someone changed it). Furthermore you seem to be confusing single hit damage with combo damage (an example of this is that Thunder has the greatest collective damage of all the spells, but the lowest per hit, while fireball and ice spear have technicaly infinite damage due to no target limit in their AoE). So since you didn't read the page, I will supply you with the info here. You would do (Spell A + Spell B) * Charge Count * Firebolt Multicharge Bonus to a single target including multiple shots assuming that target has 0 defence and protection. Firebolts multicharge bonus is 1.0 -> 1.05 -> 1.1 -> 1.15 -> 1.3 to the best of my knowledge. This would only apply if you were mixing fireball however. Furthermore Icelightning and Firelightning currently do not display arc decay in their damage,