Battle through to the point where you fight an AA wraith, a handful of Ghosts, and a standard Wraith.
You should see a silo like building. (See image) On top of this is the skull.
There are multiple methods which can be used to get onto the building.
Grenade jump.
Park a vehicle below, then jump from it onto the building.
Take a deployable cover, then use it between the red wall and the building. Move out of the way and you can use the cover as a stepping stone.
On Co-op mode, one player can jump onto the other's head, then onto the building.
Use combinations of vehicles, grenade jumps, and other players.
Drive a Ghost to the foot of the silo, then stick it with a plasma grenade. The explosion of the grenade, coupled with the explosion of the Ghost, gives more than enough height.
Notes:
If you destroy the standard Wraith, the skull will vanish.
A deployable cover can be obtained by killing the driver of the AA Wraith.
The campaign must be beaten on Normal difficulty or higher prior to acquiring the skull or it will not appear.
This may be one of the easiest skulls to work with. Once activated you have to dodge a lot more grenades, as the effect states, but you also get WAY more grenades to work with. The only difficulty with this skull is if you are driving a vehicle and you are charging into an area packed with grunts you have to be really careful not to get stuck because they have been observed throwing up to four plasma grenades in a row.
The skull will not be there when you first look for it,it's best to get the skull before the standard wraith appears as fast as you can.
Icon: A skull marked with an image of a plasma grenade.
Effect: All AI-controlled units, friend or foe, throw grenades more often, where applicable. The Catch skull has no effect on Flood, as they don't throw grenades. It should be noted that they will throw a unlimited amount of grenades at their enemies. Grunts have been seen throwing more than 4 in a row. The skull does not seem to increase the number of Kamikaze Grunts, however.
Extra Information:This Skull is good to have on in Flood levels,since the Flood do not throw grenades.
Point Multiplier: 1.5x