There are 3 secret features, all in 2-player mode.

1. Volleyball
Play level "THE COVE", with "SUDDEN DEATH" active.
Kick the any humans that appear at your opponent.
When you do this 8 times in sequence, a volleyball-net will appear.
Who-ever has the best score when time is up wins.

2. Bowling
Play a level as "ARMADON" and have both players do a "SPINNING DEATH"
at the same time. (Buttons 1 and 4, back, forward, down).
You get 10 humans as pins.

3. Glider-Q
Play level "RUINS" -Level. One players must be "CHAOS".  "SUDDEN
DEATH" must be activated.  In round 3, have a tie.  When the timer
reaches zero, a "FART OF FURY"-cloud must be present.
A parachute will appear.