Tested Kaustra on something that would not die in 2 tics, so I chose Cep-Kamuy, since it is gravitable:

Ultimate/Minikin/Cosmos

Ebullience

Used my Noctohelix build:

Pluto's/Bugard+1/-/Snow sachet
Teal/Savant/Morion+1/Moldavite
Savant+2/Savant+2/Icesoul/Icesoul
Potentia/Cognition/Nisse/Savant+1

Unfortunately, forgot to record Int inisde abyss, and bonus often change so ;_;

Dark magic skill 346

- Initial damage of 1920, then each NORMAL tick (read, every 3 seconds, unlike Helices) took around 3% of the NM's HP.
- Lasted 95 seconds.
- I think the initial damage took around 6% of the NM's HP, so probably ticks are 1/2 of initial damage.
- If we measure the duration on tics, it was 31 (+2 seconds). If the duration is related to Dark Magic skill, as was speculated, maybe it adds an extra tick every 11 Dark magic skill.

Will test more, but not being on the test server severely cuts my number of tries


Edit: Okay, maybe not 3% per tick, since it would have been almost dead after Kaustra and it was at 30-something%-40% when the effect ended. Will keep testing.