Halo Wars Skulls and Black Boxes

There is a Skull and a Black Box hidden on every campaign level. The Skulls all require killing a certain number of enemies before they appear. Here are some tips that OmniscientDeath and I picked up on our playthroughs.

• Xbox Life has the best guide for Skulls and Black boxes I've found yet, including screen shots
• Xbox Life only goes up through Mission 12 however, so for the last three, Xbox 360 Achievements does an adequate job
• Unlike Supply Crates, Skulls and Black boxes can be claimed with any unit, including air units. In fact, some are only accessible with air units.
  
• Mission 1 Look Daddy! skull: The tricky thing here is having enough Grunts available to kill. You want to be sure the Spirit dropships don't get killed before delivering their Grunty payload. I recommend rushing into Alpha base and taking out the Wraith before the Shortsword is called to extend the battle. Then concentrate on the Covenant units around the edge of the base, ignoring the ones that get dropped in until the end. Be sure to leave a unit right next to where the Skull spawns (see Xbox Life screenshots) because you have very little time after the 100th grunt is killed to grab it. It's easier to just switch to that unit with Down on the D-pad, then to try and race a Warthog back.
• Mission 5 Fog skull: I recommend not jacking Wraiths until you've killed all 5, otherwise you may run out of Wraiths that spawn.