They scan as Class VI Marshmellow Shamblers.
These mid size brutes are often found in the Times Square levels of Ghostbusters Multiplayer Mode.
Just like the mischievous cousins, the Marshmallow Mini, these Marshmellow Monsters are a not-so-tasty blend of corn syrup, water, gelatin, tetrasodium pyrophosphate, and evil.
They are to be dispersed much like the Black Slime Monsters.
The Stasis Stream can be very effective at freezing them, and then shotgunning them at close range. Otherwise, don't get close.