Catch Skull
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Level: Metropolis
Difficulty: Legendary
Text on the Screen: " Catch "
What the Skull Does: Enemies toss a lot more grenades, including two plasma grenades in almost all instances.
How to Find the Skull: Exit the highway underground and once you see a circular room with jackals and elites, you can get in the Warthog and fly to the next checkpoint. Get out and go back to the circular room from before and clear that room by killing the enemies. There's a big beam from that goes from one of the platforms to the top of the two towers. Grenade jump at the base of this beam and walk to the top...now jump over the ledge of the left tower and walk to the end where you'll see the Catch skull.