As some of you may know Lair Assault is one of Wizard's Organized Play options, and is scheduled as a single mega-encounter like some of the tournament games from Conventions of Yore.
The idea is that you create a characters of a certain level (the current Lair Assault is Level 10) using all official options in 4th Edition (Essentials, pre-essentials, from Dragon magazine, etc but not 3rd party material - just Wizards stuff). Then with 3 or more of your friends, you attempt to survive a mega-encounter that is designed to kill you.
This session of Lair Assault is called Into the Pit of Madness. Here's how it is described in detail on the Wizards website:
Mad cultists have located the Forgotten Temple of Tharizdun and sounded the dark god’s iron horn, the Wailer of Tharizdun. Now the ground trembles as the Chained God’s aspect struggles to escape. When it does, the Chained God will follow, plunging the world into Eternal Darkness.
CREATING A CHARACTER
Each D&D Lair Assault challenge will specify a level. This D&D Lair Assault, Into the Pit of Madness, is 10th level. Players bring characters of the challenge’s level to your scheduled event to participate. Characters higher or lower level than the challenge’s level are not allowed.
We use straightforward rules to equip characters for their deadly battles. Each character receives one magic item of one level higher than their level (level + 1), one of their level (level + 0), and one of one level lower than their level (level – 1). In addition, characters receive gold pieces equal to the value of one magic item of one level lower than their level (level – 1) to buy other equipment they think they’ll need. Each character may have no more than two consumable items (like potions or magic ammunition) equal to or less than the challenge’s level, and no more than one rare magic item. Note that players may equip their characters with magic items that are less than the stated levels if they so choose.
So, to use our 10th level example above, each character would have one 9th level, one 10th level and one 11th level magic item, plus 4,200 gold pieces to spend on other equipment (both mundane and magical).