In the United Kingdom, a poster promoting the PlayStation version of Tekken 3 prominently depicted a dead body with a severed leg in a morgue. In response, Britian's Advertising Standards Authority (ASA) forced Sony to remove the poster and promptly banned it, believing the ad was "macabre" and likely to cause offence. Additionally, the ASA forced Sony to have all future poster ad campaigns be examined by them prior to publication. Sony defended the ad, claiming it was meant to show "a surreal situation by positioning the body parts in the manner reminiscent of a cartoon character". Despite the explanation, the ASA stood by their decision.
Contributed by ProtoSnake
Jun was planned to be added into the arcade version of the game, but was later cut some time during development. Her data still exists within the game’s code and can be accessed using MAME cheat files. When added back in, she uses Nina’s character model and Jin’s moveset. Her voice and portrait does exist, but there are assets taken from Tekken 2.
Contributed by ShyanVixen
Anna Williams' ending shows her and her sister Nina on the beach sunbathing, when 3 men try to impress them. In the Japanese release, Nina gets jealous of Anna as she revels in the attention, so she unclips Anna's bikini top and walks away with a smile. In the international release, this scene was changed to have Anna simply walk away with the men while Nina is left on her own sunbathing, due to the original scene being considered inappropriate.

Similar scenes of nudity in the series include Tekken 2, where Anna's ending features a scene of her covering her breast while taking a shower, and in Tekken 5, where Anna's ending had Nina's body armor become dismantled, exposing her body.
Contributed by ProtoSnake
In Paul and Bryan's stage is a piece of graffiti that says "Soul Edge". This is a reference to another Namco game, Soul Blade, which was titled "Soul Edge" in Japan.
Contributed by DeerBoarDude
Harada, the producer of Tekken, originally designed "Tekken Ball" as a simulator to help people practice air juggles. Initially, a player had to hit the ball and juggle it to a basket, somewhat similar to basketball. However, Harada found the original version of "Tekken Ball" to be frustrating and decided to make it a competitive game.
Tekken 3 has a guest character in the form of Gon, a silent little dinosaur originating from a manga of the same name. His secondary costume, where he wears a turtle shell, references a time when he did so in his manga, as well as the fact that his mother was a turtle.
Contributed by Psychospacecow
If you play as either Jin or Xiaoyu 50 times, they will be wearing a school uniform. If both of them are wearing the uniform when chosen, the fight will take place on a school stage called "Mishima High School".
Contributed by Ghost
In the arcade cabinet's data, there are references to a secret character named "SAKE", though it is simply Yoshimitsu's model using Jin's move set.

Katsuhiro Harada has gone on to say that SAKE was originally planned for the game as an additional animal character, however SAKE was actually a salmon. No matter if the players punched or kicked, the salmon would simply flop around and make a flapping noise. This was removed as they were concerned that players would be angry about spending 100 Yen to play as a fish that can't do anything.

There were also plans for another character named INSECT, who would be a giant praying mantis. This is because there was a bug in the program which would make characters arms, legs and waists appear incredibly skinny, and they looked like a praying mantis. The idea was dropped as there weren't enough resources, what with adding so many other new characters.
Contributed by Dazz