Hit background characters
This really isn't so much a cheat, it's just something fun to do. If
you line up your bowler with a background character, and put the proper spin on
the bowling ball, you can actually hit the background characters! The
announcer will say "K.O.!" and the characters will disappear as you
hit them. I recommend taking Dr. Boskonovitch out!
Unlock Tekken Bowl mode
Beat the game with Xiaoyu chosen as your first character. This will unlock her school girl costume.
Choose Xiaoyu in her schoolgirl outfit by pressing start to select her. Beat the game with her as the first character in her school girl outfit.
This should unlock Tekken Bowl, which can be selected from the regular Tekken Tag menu screen.
Once you've done this, you're home free. Just go into Tekken Bowl, choose your characters, and start bowling. You even get to use a fun-filled silver bowling ball to smash gold bowling pins shaped like some weird looking guy (we think it's Heihachi). Depending on your character, you can be left-handed or right-handed, and the power of your throws varies between characters.