I like a good creature with a drawback, and this
has a very interesting one. The self-milling
part of it actually wouldn't have been a
drawback at all in the first Innistrad block
- which, come to think of it, is probably why
it's here and not there. Of course, there's
nothing preventing you from using them together,
and much like the Gitrog Monster from earlier
this week, it has an interesting design that
turns a drawback into something like a combo.
I'm still not sure whether delirium will ever be
seen in a deck that isn't specifically designed
to have four different card types in the
graveyard most of the time; but even in modern
times, few creatures are quite this efficient
for just this cost, and I certainly wouldn't be
embarrassed to cast this card.
I know a lot of people aren't exactly nostalgic
for Kamigawa block, and the Ogre/Demon strategy
was pretty badly executed, but I do sort of miss
the old philosophy of Demon design-- massively
strong, cheap thugs that come with a drawback
you have to pay. Mindwrack Demon would've fit
right in as an Oni; just replace Delirium with
"control an Ogre". It would have been a lot
worse, too, since it's far easier for your
opponent to kill your Ogres and watch your own
creatures kill you than for him to exile cards
from your graveyard.
I also like that if you don't already have
Delirium when you play him, he might give it to
you with his ETB ability... or he might not. And
if you already do have Delirium, he still mills
you for 4. Classic Demons should be like that:
powerful, but still risky.