Quote Originally Posted by Feithlin View Post
2d4 + 1/caster level = 25 average / sec. for 12 sec.
25 x (1 + 0.5 empower + 1.0 maximize) x (1.0 + 0.5 potency + 0.5 enhancements) = 125 / sec.
or (0.75 potency) 140 with clicky/pot.
18% crit for x3 adds 45 on average (I'm only using x2 because I add it to average normal damage) or 50 with clicky/pot.
Total: 170 or 190 / sec., 2,040 or 2,280 over 12 sec.

Sorry, but this is huge for only 6 sp base (granted, it's 46 sp with empower/maximize), as you just need to drop it then hide/run away. Of course, if you drop it on a mob who will die in 2 sec., this is just a bad use of the spell: why cast anything? Haste and keep your sp.
Furthermore, Melph's Arrow has no save, no SR check. This is a very good option for archers and so on. A better option than WoF now.

You can use it the economic way too. Without metas, average damage is 50 + 18 from crits = 68 x 12 sec. = 816 damage for 6 sp. Not bad, really. Sure, many SLA will be better, but the main point of Melph's Arrow is that you can hide/run while waiting for it to do its work.

Slight note to your math. Melf's is an SLA for the class, and I do believe that Eladrin said that metamagics apply free to the class SLA's, just as they do to archmage spells.