The Loki appears in the StarCraft II: Wings of Liberty mission, "Engine of Destruction". It is located in the fourth base on the right side of the map. It is dormant and invincible until a player unit moves next to it. The battlecruiser will attack units in range but will not chase for long before returning to its default position.
To take it out and earn the achievement Kicking Asgard more easily wait until the Odin is standing just Northwest the Loki's bay. Take a Viking and kite the ship over to the mech where they will fight. The Odin destroys the Loki at a loss of about 200 HP (depending on your other units in the area) and nets you the kill.
The Loki has a "liftoff" ability which grants it movement. It does not have a land ability, but appears to have a "dock" ability which accomplishes the same thing. It is also a detector though not listed.
Grants the battlecruiser the Missile Pods ability. Missile Pods deals 40 splash damage (+50 damage to light units) to air units over an area of effect.
Laser batteries are fearsome weapons across wide stretches of space, but they leave a battlecruiser vulnerable to small interceptors. The ATVX Missile Pod can show up this weakness by instantly bombarding an area with a massive barrage of anti-air missiles.