Coming on September 23, the First Blood update will see the release of a pack based on the Portal series, which includes a GLaDOS announcer, Aperture Science Wardcores, and a Portal HUD skin for the game.
Also included is a new mode, Captain's Draft, which has both teams assign a captain who must field a team from a pool of 24 randomised heroes.
The patch also contains a major change to players' inventories, renaming the Backpack to the Armory, which contains multiple filters and searching options with the aim of making it easier for players to manage their items.
Many items from the in-game Dota 2 store are being removed for sale, though these items will now be available for trading on the Steam Community Market. Valve, which hasn't listed which items are leaving the store, adds that the items may return in the return. The First Blood update will also see the introduction of new treasures.
Additionally, Medusa will now be available in Captain's Mode.
Various other balance changes have been included into the update, and players will no longer be able to adopt the fountain hook technique with Pudge and Chen--a controversial tactic which was recently used in August to great effect by Na'Vi in their match against TonFu in Dota 2 tournament The International 3.
For a full list of balance changes, check out Valve's post on the update.