Axel

In the Playground Peril level in tournament mode, shoot a missile at the middle swing on the swing set that is in the background next to the merry-go-round. A small Axel icon will be thrown into the playing area. Pick it up to unlock Axel.

Buster’s Lanes level

Get twenty kills in an endurance match.

Darkside

In the Easy Death Oven level in tournament mode, go to the sink and drive down the plumber’s butt. Go onto his leg and napalm his butt. He will blow a hole in the wall. Enter the hole to find the icon that unlocks Darkside.

Holiday Havoc level

Get thirty kills in an endurance match.

Mime

In the Holiday Havoc level in the medium difficulty setting in endurance mode, shoot missiles at the Christmas tree until it is destroyed. Get on top of the fireplace then jump off backwards and shoot a missile at the stockings. Destroy all four to reveal the icon that unlocks Mime.

Piecemeal

Successfully complete the game as Trapper to unlock Piecemeal as a playable character.

Playground Peril: Hidden health

Shoot the big duck to get a health power-up.

Playground Peril: Shoot boy on merry-go-round

You can shoot missiles at the boy on the merry-go-round from the playhouse. He will spin so fast that he will fly off.

Shock Therapy level

Get ten kills in an endurance match.

Special attacks

Freeze: Press Up, Down, Up.
Shield: Press Right(2), Down(2).
Rear Fire: Press Left, Right, Down, L2.
Drop Mine: Press Right, Left, Down.
Jump: Press L1 + R1.

Trapper

Successfully complete the game as Mime to unlock Trapper as a playable character.

Tree house: Lawnmower

Shoot the lawn mower and it will hurt your opponents. If you have the skill, get behind it and shoot, then turn around and go to the switch the lawn mower will fall in the hole and break.