I'm working on a conversion of the old 1e/2e tournament adventure "The Crypt of Istaris" for my new episodic 5e campaign. I've mostly been able to pull monsters and hazards and such from the MM and DMG, but there are a few that haven't had updates, like the iron cobra and the coffer corpse. The latter got some stats during the playtest, and Frog God "updated" them in its Fifth Edition Foes book, but I just don't really like them. They're very much a "gotcha" monster. They try to strangle people, and if you deal damage to them, they fall down as if dead ... but then they get up again and it's all like "Ha ha! And you thought they were dead! Surprise! Now roll a save vs being frightened or watch as your PC runs away screaming like a little girl!" 
There are two in a room in the adventure, and the Fifth Edition Foes book pegs them as CR 2 critters. The adventure was originally slated for "6-8 characters of 3rd-5th level". I'll have four 3rd level PCs.
They are encountered in the "Dissection Laboratory". The corpses are lying on tables with white linen sheets draped over them. They animate when a living creature comes within 10 feet of them.
What would you suggest I use in their place? Anyone got any good ideas?
Thanks in advance!
~ Jonathan
I happen to like coffer corpses. But, if you're going to replace them in a dissection lab, I'd have a "horde" of crawling claws. I think the claws fit thematically. Other disembodied attacking parts would be interesting. Great place for say, a Pennagglan rising from the table, what you thought was a vivesectioned head and guts is really...a Pennaglan! Maybe both? A Pennaglan who commands crawling claws like other vampires command rats. Yeah, that has some good creep factor.
Hmm. A swarm of crawling claws, eh? That could be fun!
Ghouls spring to mind. A horde of crawling claws definitely has an ick factor.
Two 3rd level pcs in my campaign encountered 5 crawling claws and a zombie. I was really surprised how fun it was to have the claws jump from tables to swarm the fighter. The players were really creeped out.
I was also surprised that they managed to whittle away 12 hit points from the already injured fighter. (It took the bard a few rounds to realize he should use his aoe Thunder cantrip to harm his buddy, but also kill the claws).