Killzone: Mercenary's biggest addition to the series' gameplay is a "wrist-mounted murder assistant," the Van-Guard, which allows players to unleash special weapons by tapping on the PlayStation Vita's touchscreen, said art director Tom Jones on the PlayStation Blog.
"What we've tried to do, essentially, is create a Vita on the wrist in-game," said Jones in the video interview above.
The mechanic works in both the campaign and multiplayer modes, letting players bring in attacks like an Ion Cannon to electrocute enemies or camo for stealth. In multiplayer combat, they function similarly to killstreaks, but a cooldown timer ensures they can't be abused.
Melee attacks also take place on the PS Vita's touchscreen, with simple swipes enabling players to employ vicious tactics like stabbing an enemy in the kidney.
Killzone: Mercenary launches Sept. 17 in North America. For more, check out our preview from January.