According to producer Katsuhiro Harada, SEGA offered a free Virtua Fighter character to be added into the game if the game was ported to the Dreamcast.
Contributed by ZpaceJ0ck0
When porting the game to the Playstation 2, the developers portrayed each of the characters' teeth with polygons. Years later, Harada, the producer of the Tekken series, looked back and thought that "it was a total waste of polygons."
When using a team consisting of Kazuya Mishima and Devil, Kazuya will be seen on his own in the pre-battle animation and when tagging out to Devil and vice versa, Kazuya/Devil will instead transform into their partner, as they are the same person.

The same is not true however for an Ogre/True Ogre team.
Contributed by MightyKombat
The console version of Tekken Tag Tournament is very different from the arcade version.

The arcade version was simply an upgrade kit for Tekken 3 and ran on the same 32 bit engine, utilizing the same graphics. However, when ported to the Playstation 2, it received a huge upgrade to the graphics along with upgraded music tracks, additional stages and music to go with them.

The 2 versions play similarly, although there are some noticeable differences in gameplay, such as some attacks being more efficient in the arcade version and vice versa.
Contributed by kaidos123
Dr. Bosconovitch can be found amongst the cheering crowd in Tekken Bowling mode, where he can be "K.O."ed if you aim and throw the ball at him.
Contributed by kaidos123