From Destinypedia, the Destiny wiki
Invasion Battlegrounds are three-player Arena matchmaking activity that were released with the Dread episode. In it, Guardians assault Hive positions all across Sol and hunt down the leading Hive commander and destroy them before they establish permanent footholds for the Weavers of Sorrow.
Invasion Battlegrounds function more closely to the original Battlegrounds within Season of the Chosen with each section possessing a progression system for each encounter. However, unlike previous battlegrounds, encounters are randomized, irregardless of the location and the boss connected to the Invasion Battleground. One encounter requires Guardians to gather Soulfire crystals from Soulfire Bearers to survive a Tomb Ship bombardment, another requires to stop Hive from sacrificing themselves to a ritual portal to summon an Invasion Ogre, another requires to kill hordes of Hive, or another to survive an assault from a Corruption's Claw mini boss. Each battleground requires the players to complete two of these four objectives before reaching the boss room.