Damaging a priority target (elite+ enemy or guardian in super) or using a powered melee attack on an enemy will highlight them. Defeating a marked target grants grenade, melee, and class ability energy, and increases weapon reload speed and stability for you and nearby allies. Additionally, marked targets leave a cloud of weakening smoke when defeated that grants Invisibility to any allies that pass through it. After exiting Invisibility, (non-boss) targets you damage will become marked.