Grat are fought as random encounters within the Garden Training Center, all around the Garden as random encounters during the Balamb Garden Revolt event, and in a fixed battle at the library at this event, summoned by the Garden Faculty.
Grat uses Vampire that inflicts damage and restores Grat's HP equal to the amount of damage it inflicted. Its Gastric Juices is a physical attack that may inflict Poison the player, though this attack can be avoided with high evasion and luck. The chance of it casting Gastric Juice as well as inflict Poison increases as the player levels. Sleeping Gas is used sometimes as counterattack if Grat is physically or magically attacked, and this may inflict Sleep on all party members.
They are weak to Ice and Fire. Grat is a good source of Sleep and Silence magic early in the game; Sleep is useful against the T-Rexaur, a tough monster rarely encountered in the Training Center as well.
In the 2000 film version of Charlie's Angels, the two boys are playing Final Fantasy VIII and are controlling Squall and Quistis in a battle in the Training Center. They are fighting against two Grats and one of the Grat is seen using the Vampire ability.