So since they are trying to take over another world/plane, I figure I would give you a look behind the curtain. Know thy enemy!!! Some of you may or may not know the characters talked about. But you will recognize some of the names used on cards...past and present.
Phyrexia, I believe, was Magic's first attempt at 'making' a Hell. There are 9 levels or Spheres inside each other.
Level 1 (surface) - For the most part a model day junk yard. It has furnaces that throw ash into the air from recycled artifacts. If you think of how old Mirrodin was with oily shit all over the place...that is how it looks.
Level 2 - This is the waste level from level 1. All the compacted debris from level 1 goes here. All of Phyrexia's ammo is held here.
Level 3 - This 'PROTECTIVE' level of Phyrexia. This is a level of twisted pipes and plumbing. It goes without saying there are more then just gators in these sewers. The pipes contain spatial distortions that prevent 'true' planeswalking to the lower levels.
Level 4 - This is where some of the great furnaces are and where most of the phyrexians live. This is also where new phyrexians are 'born'
Level 5 - The is home to the phyrexia's deadliest weapon. The Sea of Glistening Oil. This is the corrupting substance that is the life blood of any phyrexian and will twist any natural creature into a phyrexia.
Level 6 - This would be the VIP section of phyrexia. This is where Yawgmoth's minor and pawns live.
Level 7 - HELL...plain and simple. This is the punishment level of phyrexia for interrogation, experiences, and...fun. Phyrexian Gremlins and Yawgmoth Demons are the masters of this level. They are great at destroying artifacts and artificers.
Level 8 - The Abyss. It is rumored to be a void where nothing escapes. But to a few...it is most plentiful source of black mana in the multiverse.
Level 9 - The is the Sanctum of Yawgmoth where he is a god over anything on/in Phyrexia. This is also his prison.
Not getting to much into the details (more myths to come). Each ruler of Phyrexia wants to expand. Without being a true planeswalker, you could not enter or leave Phyrexia (past level 3), as a whole. But through sacrificing people and artifacts then using MASSIVE amounts of mana, one could open a portal to another plane without going through the Blind Entities.