Behemoth slimes look very much like normal Slimes, only much, much larger. Their faces, the usual round eyes and goofy grin combo, have not been enlarged at the same rate as the rest of their body and appear rather small by comparison.

It is impossible to synthesize a behemoth slime: they must be scouted on an uncharted island that is inhabited only by Slimes and She-Slimes. The uncharted island is between either Palaish or Xeroph and Domus Isle. Behemoth Slimes have the same ability as normal slimes, but synth two together and voila! You get a King Slime. Also if you synth a sheslime with it you get a, you guessed it, a shebeomoth slime.