In this post, I’ll demonstrate how to compare Molag Kena to Nerien’eth on a single target. I'll provide an example using my magicka sorcerer.

The image for Nerien’eth was taken without CP. The tooltip is increased by both Elemental Expert and Thaumathurge.
My Max Magicka and Spell Damage with Nerien’eth is 43486 and 3189, respectively. The spell damage is with Major Sorcery and 3 Sorcerer abilities slotted. Molag Kena provides 129 Spell Damage and an additional 516 Spell Damage when proc’ed. I estimate a maximum uptime of Molag Kena at 86% (6/7 as you cannot re-proc it when it is active). This means that the maximum Spell Damage from Molag Kena is This is increased to 722 Spell Damage after taking into account Major Sorcery and 3 Sorcerer abilities (6% increased Spell Damage from Expert Mage passive). Based on my Max Magicka and Spell Damage, this corresponds to an increase of ability tooltips by ~9.8% So we can roughly say that we would expect a DPS increase of ~9.8% with Molag Kena. This is an approximation since Light Attacks depend more on Spell Damage than abilities so will be increased by more than 9.8%.
There are two ways to determine the contribution of Nerien’eth. One way is to look at a parse. In the example parse below, we can estimate the DPS increase of Nerien’eth by dividing the total damage contribution of Lich Crystal by the total damage dealt less the damage done by Lich Crystal. For the example parse below it turns out to be ~9.8%, similar to the estimated upper bound DPS increase with Molag Kena. The method above does depend on the RNG or a particular parse so a theoretical approach would be beneficial. The DPS contribution of Nerien’eth can be modelled by first modelling the number of attacks required proc Nerien’eth with a geometric distribution and then we will be able to obtain the uptime of Nerien’eth and finally estimate the DPS from the uptime.
I first tested the validity of a geometric distribution with in-game testing. I counted the number of attacks required to proc Nerien’eth and made the following image The median number of attacks required to proc Nerien’eth is which means that the median amount of time required to proc Nerien’eth is Since you cannot have two Lich crystals at once, the internal cooldown of Nerien’eth is estimated to be 3 seconds. Thus, I would expect one Lich crystal every From my parse above, I did 84 non-DoT attacks over 35.5 seconds which means the number of non-DoT attacks that could proc Nerien’eth is 2.37. So I would expect one Lich crystal every The average damage for each Lich Crystal is Let’s say I have 100 in Elemental Exper (25%) and 2 in Thaumathurge (1.6%) and my spell critical is 71.2% and my critical modifier 0.62 then the average damage for each of my Lich Crystal is So my expected DPS with Nerien’eth is 2319 (13385/5.77) which was reasonably close to the example parse. Based on this, I conclude that Nerien’eth is comparable to Molag Kena for the rotation shown in the parse.
Additional note: I considered making a comparison between Molag Kena, Nerien’eth and Skoria but there is something very peculiar about Skoria. It appears that DoTs must be running for some period of time before it can actually proc. I counted the number of Puncturing Sweep hits required to proc Skoria and found that for the first few hits Skoria will never proc. This is shown in the image below. A similar result can be obtained when using Elemental Blockade (data not shown)