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 crest of the hidden skull on this level appears to be the Covenant, Mark of Shame. Judging by this seems the level will have a Covenant environment or the Flood controlled High Charity.