What are skulls on halo reach?
the primary ones are: iron skull, black eye skull, tough luck
skull, catch skull, cloud skull, famine skull, thunderstorm skull,
tilt skull, mythic skull
and the secondary ones are: blind skull, cowbell skull,
gruntbirthday party skull, iwhbyd skull
and all of them are accessible from the start so you dont have
to look for them.
hope i helped :P