Krysta is a boss from Final Fantasy VIII, encountered on the Terrace of Ultimecia Castle. It is one of Ultimecia's eight minions. To get to the Terrace the party must cross the chandelier from where Sphinxaur was battled, but it must be fixed it place via a lever in the floor below or it will drop when stepped upon.
Counter Rocket is a counterattack to all moves which damages according to characters' Vitality stat. When defeated, Krysta will cast its final move, Ultima, which will hit all characters, doing especially devastating damage to those with low Spirit. The player can draw Carbuncle from it if it was missed earlier.
Due to its relatively low HP, Krysta is easy to defeat with just one attack. Casting Meteor, preferably in conjunction with Double or Triple, will most likely kill it right away. Another strategy is summoning Diablos, then Cactuar; if both Guardian Forces are at a considerable level, Krysta will be defeated after these two attacks.