The Denebian Slime Devil
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"When encountered, a Denebian Slime Devil appears as a hideously grotesque thing, often culled from the deepest fears and anxieties of its preferred victim. However, this is a deception, for the creature’s true form is that of rancid, flowing anthropomorphic ooze composed of disgusting refuse gathered from the scum of the dankest swamp. Sages have been unable to identify a practical purpose or ecological service provided by a Denebian Slime Devil."
"If a Denebian Slime Devil is struck by a weapon it immediately splits into 1-4 identical copies of itself, each immediately attempting to locate its own victim. Each copy has the same abilities, and number of Hit Points as the original."*
Now substitute for 'Denebian Slime Devil' the terrorist group known formerly as ISIS (but shall henceforth be known as the name they hate: Daesh); substitute 'struck by a weapon' with 'bombed', and you've pretty much got it.