The Merchant Ship Frontier salesman's appearance will permanently change after you purchase all four "cowboy parts" from the shop. To unlock the cowboy items for purchase, you must first purchase all other parts first (these also typically require unlocking). Do not purchase all the cowboy parts if you don't want the salesman's appearance to change for the duration of the game.
While holding down the Z button on the character selection screen for battle mode, press A to be able to select the CPU characters.
Successfully complete the game to change the title screen to display one of Pommy's different levels with a blue background with clouds.
Win the gold cup in survival mode to unlock battle royal mode.
At the battle mode character selection screen, hold Z and press A to use the CPU characters.
Win the gold cup in king and knights mode to unlock key trial mode.
Win the gold cup in battle royal mode to unlock king and knights mode.
Win the gold cup in key trial mode to unlock score attack mode.