Elements

The Tekken series uses separate buttons for right and left limbs, resulting in four buttons. Other trademarks include throw escapes, and starting from Tekken 2, autoblock. Each iteration was improved upon both graphically and technically. Tekken 3 introduced the ability to move into the foreground or away from the background, commonly referred to as "sidestepping." Also, Tekken 3 reduced recovery time after being knocked down than previous games and each game afterwards include rolls to recover instantly after hitting the ground, allowing the player to get back into the fight instead of pounding buttons. Tekken 4 gave characters even greater mobility by adding true 3D movement while simultaneously including geometrically complex arenas with unleveled ground, obstacles, and walls. This differed from previous Tekken games, where all of the arenas were level and contained no boundaries, meaning the player could walk forward or backward without limit. Tekken 5 saw the return of both walled and infinite arenas, with the fluid mobility of Tekken 4 being toned down to appease many players who felt it made the game more focused on evasion. Tekken 6 retains much of the design from Tekken 5 but also includes "Rage" mode (when a character is near the end of their vitality bar, they earn a damage multiplier) and "Bound" hits (hits that, when connected with an airborne opponent, will place them in a grounded state where they cannot escape for a certain period, allowing combo extensions). Tekken 6 also has destructible floors that allow the fighters to fall through to new fighting areas when broken. Since Tekken 5, customization of the characters has been made possible via fight money earned in matches. Players can purchase clothes and accessories to display on their characters during future matches.
Tekken Tag Tournament, released between Tekken 3 and Tekken 4, is not a part of the Tekken storyline. The game allowed each player to control one of two selected fighters, who could be tagged in and out of the fight by the additional fifth button, which can be used for tag team attacks and juggles, amongst other tactics. Otherwise, Tag Tournament used much of the Tekken 3 gameplay engine and reintroduced characters who were not available since Tekken 2. Tekken Tag Tournament 2 continues the spirit of the original Tekken Tag Tournament with two-on-two battles while also incorporating some of the gameplay features of Tekken 6 (such as the aforementioned "Bound" hits). New features for Tekken Tag Tournament 2 include simultaneous dual-character combos (being able to tag in a character then have both characters juggle their opponent onscreen before the tag is complete).

http://en.wikipedia.org/wiki/Tekken