The beta will feature about 90 minutes of gameplay (assuming you don't die over and over), and will actually have two boss characters to fight. One will be at the end of the "main route," while the other can be discovered by traveling down the "sub route."
Unlike the main game, the beta will only give you access to six pre-defined characters: soldier, warrior, sorcerer, temple knight, dual swordsman, and hunter. And unlike other "betas," Namco Bandai promises that this is a real beta, testing the game's online functionality before launch.
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The main features to be tested are blood messaging and blood stains. Their purpose remains largely the same as in the original Dark Souls. However, in Dark Souls 2, you don't have to use an item to leave a message. Instead, you can simply press Start and choose "Blood Messaging" to place messages at any time.
The beta will also test summoning and co-op play. By using the "white sign soapstone" item, players can summon others to help--but the amount of help you'll get will be determined by the size of the soapstone and the number of enemies you're encountering. The more enemies the game expects you to fight, the longer the summon should last.
Covenants will also be tested. In Dark Souls 2, if you get invaded by another player, you'll be able to automatically summon a sentinel to assist you and "rescue" you. This will theoretically prevent abuse by high-level players that repeatedly invade the games of new players. However, there will also be other covenants to encourage you to be an invader.
Finally, the beta will give players a chance to see how being undead is changed in Dark Souls 2. Dying consecutively will actually lead to the depletion of maximum HP. As you constantly revive at the bonfire, you'll notice your health bar steadily shrinking. In addition, your appearance will start changing. The more often you die, the more haggard you'll look--until you look like a zombie. You'll be able to undo the effects of undeath by using a human effigy--but do note that those are a finite resource. "There is no easy way out this time," From Software pointed out. "Generally speaking, players want to stay alive, not undead... the intention is the struggle to stay alive."