Heretic

The Heretic level is a map to featured in the Mythic Map Pack along with 5 others. Also it is known that this map will boast an Energy Sword. It can be assumed that this map will be good for Team Slayer.

Skull
The logo of the hidden skull on this level appears to be a Forerunner or Covenant symbol that looks like a speed gauge.

Trival

 * N/A