I like this concept a lot. This could be a lot of fun to play with my PCs. Getting them addicted and then fleeing the scene. I am always interested in reoccurring monsters and this one certainly has a nice dark side to it.
The scope for all of the other drugs is really cool and sparked my imagination as to what they would be like.
I really like this monster. The mechanics are interesting - too many witches inflict my monsters with misfortune it would be fun to get them back. And it has quite an easy insert into an urban campaign.
A little OP, especially with the large resistances but nothing a good party could not handle.
I like this monster. I was walking home today and thought about the person in front of me getting snapped up into extradimensional space by one of those things. It is always the prostitutes and vagrants that get the short end of the stick,
That said I had to re-read the first description a couple of times and it does seem that the monster would be better if it did not require air.
Still something I wouldn't mind ambushing my PCs with. It will get my vote.