There are several different types of abilities, and they all have their own unique function. They can be activited by clicking on them or by pressing the corresponding number key shown, which is determined by the order you acquire the abilities in. You also spawn with a random ability if your class is "A.I." Using an ability does not consume a turn. You gain an ability by siphoning an ability block. These blocks show the number of enemies that it will spawn once siphoned, much like score blocks. The number is not random and depends on the ability, with ATK being the highest cost at 8.