The royal armor is a great example of this as well as the arcane staff ability (I think they are the only ones left with this mechanic), it can make some interesting and niche builds, I would like to see more of this mechanic as I believe it can be used to counter prolonged fights or even healers in 1v1.
i would also like more attrition gameplay options that arent purely based on dots
but in this special case - mana drain - its not possible to balance i think
even before the addition of lymhurst cape, increased popularity of royal cowl etc. nobody used mana drain comps (saw like 1 HG vid with successful mana drain comp and it seemed like their win was more thanks to skill difference)
we have way too many options to get mana back
if u wanna make mana drain a viable option it would be either easily countered or super strong im afraid
stuff like royal armor or arcane mana drain channel could get additional effects like "target gets 20% less mana from all sources for the next 10s".
so not only "steal mana/make lose mana" but other effects. real debuffs. i would like a working version :).
and while were at it: give us some hexes like "next (only Q and W) heal on target deals damage instead / drains x mana from healer / silences healer for 2 seconds" please
Yeah the druid cowl helm has suffered with all the energy options as well it is a dead item now and mise well be reworked.
Maybe items like curse staffs can get additional utility like drain mana from enemy or it drains yours (skills cost more energy). All in all I agree with Kayl and it might not be worth making more items but instead re-work the existing ones into doing something else, but ye hate to see items see no-use because of mechanic not being relevant anymore.
Warlock feels lacking in the debuff department and also lacks CC of any relevant kind. Energy drain would be a nice niche, maybe.