Note: This cannot be done online. Have no Green Herbs in your inventory. Find a Green Herb and press Y + A to pick it up while using it. If timed correctly, the game will now show you as having 300 Green Herbs.
Try these costumes for a change! Have fun!
If you want to use a character's loadout so every other character can use it, score rank A or higher on all missions up to 5-5 with that character.
Make sure that you have zero green herbs in your inventory. Locate a green herb and pick it up while using it (on the default control scheme, press the Y and A buttons simultaneously). If your timing was correct, the game will have tried to subtract one herb from a total of zero. This will cause the inventory counter to cyclically roll backwards to its maximum amount, resulting in 300 green herbs available for use. Note that this method will not work online.