OK. Had to do a new play through to see if this would still work. It does, but not as well as I remember.
Fire blobs have a weakness to water. If you strip their physical armor and get them wet (Rain, water balloon, etc) they get the decay status which means you can heal them to death. Wet only lasts 1 round in all that fire, so you have to keep applying wet if you are going to use this tactic. It can be highly effective if you group has skill in Hydrosophist.
I seem to remember that while they had the decay status the fire blobs would take damage traveling through fire. Perhaps that was classic edition or perhaps I don't remember correctly. Either is equally likely.
Another trick would be to abuse rupture tendons and teleport the blob as far away as you could. It should kill itself trying to get back to you.
While it is "technically" a level 13 fight, given the level of the creatures, if you are playing on Tactician, wait until level 14 to make it go easier due to better stats and better gear. If that doesn't work, then delay until level 15 (already mentioned) and you should be able to stomp it.
