TheGameSite: Tips, Cheats, Walkthroughs: N64: All Star Baseball 99
ABBTNCSTLO: Fat & Skinny mode. Makes some players very skinny and others very large.
BBNSTRDS: Big Baseball mode. Makes the ball really big!
GRTBLSFDST: Smoke Trail mode. Baseball leaves a trail of smoke behind it.
LIZARD TRICK
While playing in a normal game, in Kaufmann stadium (Kansas City Royals), there are two signs that say "Win a Lizard." If the player hits one of those signs while batting, his team will turn into lizards.
CHEATS
Enter the words as they appear. There are no spaces to insert, and there is no choice for upper or lowercase letters. If the game is turned off or reset the Cheats will need to be reentered.
ATEMYBUIK: Alien Abduction mode. After entering the code, start an Exhibition or Quick Play, select a stadium, and scroll to the bottom to "Alienapolis Park." The home team will have the same stats as the team that was picked during set up, but the players will now look like aliens.
GOTHELIUM: Big head mode. Gives the players big heads, hands, feet and bats.
PRPPAPLYR: Paperman mode. Makes the players very thin.