Ken Griffey Jr.'s Slugfest cheats and cheat codes for Nintendo 64

Fireworks
Choose exhibition mode. Go to the stadium selection screen, after
enter "View Stadium" mode by pressing Z. Then, hit R + Z.

Exploding batter
Hit Right, Left, Down, Right, Left, Up, Right, Left, Down buttons
while in the batter's box.

Create a new player and enter the following cheat codes as name.
If the code is accepted, you should hear a sound.

Invisible team: Enter "CODE INVISIBLEMAN" as player name.
Thin team: Enter "CODE TOOTHPICK" as player name.
Flat team: Enter "CODE STEAMROLLED" as player name.
Small team: Enter "CODE LIDDLELEAGUE" as player name.
Weeble team: Enter "CODE WEEBLEMAN" as player name.
Full attributes: Enter "CODE SUPERHUMAN" as player name.
Big bats: Enter "CODE PHATTBATT" as player name.
Big feet: Enter "CODE BIGFOOT" or "CODE BIGFEET" as player name.

Unlock Team Nintendo or Team Angel Studios:
Enter "CODE EMOTIONS" as player name.
or
Win 1st place on the World Series with any team

Enable big head mode:
Win 1st place on the World Series on the rookie difficulty level. 
After, create a new player and enter "CODE BIGGHEDZ" as player name.

Tick team
Win 1st place on the World Series on the veteran difficulty level. 
After, create a player and enter "CODE THETICK" as player name.

CPU vs. CPU mode
Win 1st place on the World Series on the all-star difficulty level.
After, create a player and enter "CODE CPUVSCPU" as player name. 

Homerun
Hit Left, Left, Right, Right, Right, Left, Left while in the 
batter's box with Ken Griffey Jr. before the pitcher winds 
up to throw the ball. Ken Griffey Jr. should be point his bat in
the direction where the ball will be hit. After, connect with 
the ball to automatically hit a homerun.