Heretic

Heretic is a multiplayer map for Halo 3, it will be released with the Mythic Map Pack along with 5 others. It is suspected to be a remake of Midship. Somewhere in the map, there's a Sky Box and there's a window that you look out from the Belly of the ship (Which you are on) and when you look out, you see acouple of Covenant Assault Carriers, and other ships moving towards a System and its possibly our Solar System. You can get a very good, Detailed view of the nearby ships. There's also a Planet nearby. The Energy Sword on here spawns somewhere that you use a Jump pad to get.

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

Trivia

 * The term "Heretic" is used by the Covenant Loyalists to refer to the Covenant Separatists, hinting that this map may feature Covenant Separatist structures. This map could also be based on the level The Arbiter from Halo 2, as the Gas Mining Facility featured in that level was controlled by the Heretics, and thus could be a remake of the Halo 2 map Colossus.
 * Getting a Sword Spree medal on this map earns the player the 'Blades of Fury' achievement. This fact suggests that it is either a small or medium sized map.
 * Rumors saying Heretic might be a remake of Midship
 * This might be the first map to have Plasma Grenade start-out for Halo 3 Multiplayer.
 * This map, Longshore and Citadel are not confirmed to come out with the Mythic Map Pack. Go here for details.