Due to experiments conducted on him for two years, Jak has also gained the ability to manipulate Dark Eco to transform into a darker version of himself known as Dark Jak. The form is only accessible after Jak has absorbed enough Dark Eco to charge his ability. Dark Eco drops from slain enemies and can occasionally be found in red crates scattered throughout the world. In his Dark form, Jak becomes much more agile and his melee attacks become more powerful but he loses the ability to use the Morph Gun. Jak 2 also introduces a "currency" known as Metal Head skull gems. By collecting these skull gems which are dropped by most Metal Head creatures when defeated, Jak can gain additional abilities for his dark form and play minigames at kiosks throughout Haven City. The Dark Jak abilities that can be unlocked can be used to unleash devastating attacks that kill all enemies within the vicinity at the cost of ending his Dark form immediately after the attack.