Microsoft adds Pipeworks’ fighting game, Dead Block, and MLB Bobblehead Pros to XBLA; Games on Demand adds Two Worlds, Sacred 2, and Risen.

In two weeks, Microsoft will invite gamers to its annual summer bash, commencing the Summer of Arcade promotion with Supergiant Games’ Bastion on July 20. However, the action is heating up today on Xbox Live, as Microsoft has added three new Xbox Live Arcade games and three Games on Demand titles to its virtual marketplace.

Leading the pack today on Xbox Live Arcade is Deadliest Warrior: Legends (800 Microsoft points, or $10). A follow-up to last summer’s tepidly received Deadliest Warrior: The Game, the new installment is also based on the television show Deadliest Warrior.

Deadliest Warrior: Legends gets bloody today on XBLA.

In Legends, gamers will control deadly warriors and take on famous figures like Alexander the Great, Attila the Hun, Genghis Khan, Hannibal, Hernan Cortes, Shaka Zulu, Sun Tzu, Vlad the Impaler, and William Wallace.

The game offers “enhanced” graphics, nine arenas, new fighting moves, and an all-new Generals strategy game, where players will battle on a larger scale.

Also out now on XBLA is Candygun’s Dead Block (800 Microsoft points, or $10). The Unreal Engine-powered game lets gamers play as a construction worker, traffic warden, or a pretty peckish boy scout. Players are tasked with surviving waves of oncoming zombies either by force or with strategy. Additionally, gamers can fight alone or with friends in the split-screen mode.

The last new XBLA game out now is MLB Bobblehead Pros (800 Microsoft points, or $10). A Major League Baseball-licensed game from Konami, Bobblehead Pros includes all the league’s teams and players. Additionally, the game sports co-op and online battle modes.

Switching to the Games on Demand hub, Microsoft added three new role-playing games to that tab this week. 2007’s Two Worlds ($20), Piranha Bytes’ Risen ($20), and 2010’s Sacred 2: Fallen Angel ($30) are now live on the download hub.

Reinforcing what we’ve previously heard, a new report states that free-to-play games are coming to the Xbox 360.

Develop says multiple sources have indicated Microsoft is talking with developers about bringing F2P titles to its home console. Xbox Live will add a microtransaction service that would allow in-game items to be bought “on the fly.” That likely means items could be accessed immediately without having to restart the game, a process that would otherwise severely inhibit such games from catching on.

Free-to-play games traditionally rely on microtransactions (and sometimes advertisements) to support themselves. Anyone is able to play the game for free, but players are encouraged (but usually not forced) to make purchases of things like additional levels, cosmetic items, new weapons, etc.

No time frame was attached to any of this. A similar report in April said free games would begin showing up on 360 in 2012.

PlayStation 3 is already home to one free-to-play game, Free Realms. Nintendo has flat-out said, “Nintendo is not interested” in microtransaction-based games. Steam added support for F2P games last week, and Valve just yesterday announced that Team Fortress 2 would be permanently made available for free.

Many of the big F2P games out there are MMOs, a genre that has in the past not enjoyed a tremendous amount of success on consoles. There are other styles of games that rely on microtransactions, as Facebook games demonstrate. Zynga’s entire line of titles, including the likes of the massively popular FarmVille and CityVille, are free to play, although the developer has already stated it’s unlikely its games will come to Xbox Live due to the relatively small userbase it has compared to Facebook.

Chief game designer Brian Reynolds explained earlier this year that Zynga is “after a lot of demographic” and that Xbox Live is “too small a demographic.” Not having enough people limits “the number of anyone’s friends that’s going to be able to participate in the social experience,” something that is key to its games’ success.

Ubisoft recently announced the free-to-play Ghost Recon Online for PC and Wii U. The latter version may not end up being free due to Nintendo’s stance on the subject but it seems like a potential game for Xbox 360 if the reports of F2P support turn out to be true. The same can be said for Electronic Arts’ line of free Battlefield titles, such as Battlefield Heroes and/or Play4Free (pictured above).

Microsoft has been working hard to make the 360 accessible to more people. With the addition of more and more media functionality and Kinect, free-to-play games could very well be a good way to attract consumers to the system that aren’t necessarily interested in dropping $60 on a retail game