Chrysalis beasts, or "chrysalides", were genetically altered creatures that appeared in Star Wars Legends canon. Long before the age of the Galactic Empire, the Sith had utilized Force alchemy in order to alter living creatures to suit their purposes. The knowledge of such practices was encoded on holocrons which would be buried on Sith-controlled worlds, the secrets becoming lost to time.
However, Emperor Palpatine would employ Sith alchemy to produce chrysalides following his resurrection in 10 ABY. He engineered several Chrysalides from rancor specimens which he used to protect the Imperial Citadel on Byss. The mutated rancors seemed to be invulnerable to the weapons used by the New Republic commandos and X-1 Viper droids storming the citadel and the beasts' teeth were capable of rending through the armour plating of the Viper droids. They turned the battle in the Empire's favour and caused the surviving New Republic personnel to retreat.
Chrysalides would attack anything in sight apart from other Chrysalides, and would almost always prioritize the largest available target. Other creatures mutated into chrysalis beasts were gundarks, katarns, and vornskrs.