Play as Bam Bam Bigelow or Yokozona (PAL version):
Press Up, X, Down, B, Y, R, L, A(2), X, Y at the copyright screen.

Hint: Pin earlier in match:
Work your opponent down to slightly below half energy. Then, get him down on the mat, press X to pin, and immediately hold Up + Y. The referee will count to three and your opponent will not be able to leave the mat. Note: This will not work in Tag Team or Survivor Series modes.