PS1 | Submitted by anonymousEvery level type
Go to the options menu. Press L2 R2 L2 R2 L2 R2. Now pick a level. It should then say Level Type. You should be able to pick all three level types.
PS1 | Submitted bySelect Level
At the option screen press L1, R1, L1, R1, L1, R1. To play original pong select the star field beyond the final level
PS1 | Submitted byGet levels
Go to the zone select screen and pause the game. For level 1 press L1, R1, L1, R1. For level 2 press L2, R2, L2, R2. For level 3 press and hold L1 + R1 + L2 + R2
PS1 | Submitted by GarrettSecret Zone
Beat the game to unlock zone 8. Zone 8 is classic pong