I like the idea of having a max HP reducing creature, but this mechanic belongs to
as a core theme.
There is nothing that says it can't be moved somewhere else, but I think it would be good to give some kind of a link to darkness element.
What do you think of something like:
"Serpent's attacks also reduce your opponent's maximum HP if your mark is
.
: Devour "
or
"Serpent's attacks reduce max HP instead of current HP or both if your mark is
.
: Devour"
Reducing maximum HP is only really useful right now if have enough sources of max HP drain. SoV would definitely benefit from the synnergy and needs a boost, but reducing only max HP and not both current and max HP makes this creature somewhat less effective.
Also remember that max HP drain will not kill your opponent in and of itself... It can leave them with a single HP but you still have to deal that 1 point of damage.
I think it may be better to have the max HP reduction be in addition to reducing current HP rather than instead of reducing current HP. Then this creature would be very useful and effective.
As it stands right now, it is a very cool and unique idea, but I don't think I would use it outside of a shard of void deck. That is basically a forced combo which is not usually a great idea since it tends to make a card too situational.
