Me and my bro got all three skulls
Sandbox was tough, we had to use several Pipe Corner pieces after several failed tries, the towers in the back of the map were firing at the elbow of the corner piece while we slowly reached the skull, i placed several corner and regular pipe pieces until i got close enough to pick up the skull, my brother died when the beam hit him, i was the only one there with the skull, i ran to the back of the pipes i had placed where i was safe, my brother came up with this brilliant idea, he placed a two way teleporter in Sandbox while i place ones in the pipes, i was able to hold onto the skull while i was in Monitor mode, so i teleported to him and gave him the skull, so now we have all the current unlockable skull achievements :D
