The following blades become available when you perform the corresponding actions.
Bamboo Shoot Blade:
Play a full game of Zen mode every day for 5 days.
Butterfly Knife Blade:
Get a combo with a Strawberry 40 times.
Slice 50 Bananas.
Get a combo in Zen mode after the timer stops.
Slice 20 Freeze Bananas in Arcade mode.
Mr Sparkle Blade:
Lose Classic mode with a score of 42.
Old Glory Blade:
Lose Classic mode with a score of 50.
Party Time Blade:
Slice nothing but the Strawberries in Arcade mode.
Get 100 Critical Slices.
Pixel Love Blade:
Follow Halfbrick Studios on Facebook or Twitter.
The Shadow Blade:
Get a score of 175 in Zen mode while upside-down.