From a older rpg WIP project of mine,
I'm not found of the "just blobs" myself. So I've been creating based off of creatures who are naturally slimy.
Sliumg, like slugs, do not take well to cold environments and are sensitive to salt. They prefer warmer environments so their gelatinous bodies can keep a smooth locomotion. The more humid/warm the environment = faster they are. However at a certain point the heat will shrivel them up.
I was going to make them one of those "base" creatures that would have many variants of elements but I like the idea as a species that they just can't process minerals well. So in order to defeat these creatures in a logical amount of time (as they have crazy high defense) you must overwhelm them with salt, cold or heat- basically cause an allergic reaction.