Here’s the Bonus Fields and Bonus Characters strategy guide for “Mario Super Sluggers” available on the Nintendo Wii.

Bonus Fields:

Successfully complete the indicated task in Challenge mode to unlock the corresponding field.

Bowser’s Castle: Defeat Bowser in Challenge mode.
Bowser Jr. Playroom: Defeat Bowser Jr. at that stadium.
Daisy Cruiser: Buy the cruiser pass from the shop at Peach Ice Garden.
Luigi’s Mansion: Buy Luigi’s flashlight from the shop at Mario Stadium.

Bonus Characters:

Successfully complete the indicated task to unlock the corresponding character. Note: There are multiple ways a specific character can be unlocked.

Baby Daisy

Use Wario’s magnet to pull Daisy’s baby rattle from the fountain at Peach Garden. Then, have Yoshi go through the manhole cover on the left side of the garden to find a crying baby. Give Baby Daisy the rattle to unlock Baby Daisy.
Baby DK

Use Yoshi’s power at DK Jungle to free Baby DK from the palm tree to unlock Baby DK. Alternately, defeat DK’s team.

Baby Luigi

Pull the levers in Mario’s Stadium to connect the bridge to unlock Baby Luigi.

Baby Mario

Unlock Baby Luigi, then save Baby Mario at the field where you battle Bowser Jr.’s team to unlock Baby Mario.

Baby Peach

Use Princess Peach’s heart power on the grass Toad statue at Peach Garden to unlock Baby Peach.
Birdo

Defeat Bowser Jr. at Yoshi Park to unlock Birdo.

Blooper

Have Princess Peach use her heart power on the bubbles in the water at the dock in Mario Stadium to unlock Blooper. Alternately, successfully complete all tutorials in Practice mode.

Blue Noki

Successfully complete Blue Noki’s task at Mario’s Stadium to unlock Blue Noki.

Blue Pianta

Get the key, and save Blue Pianta from the shop at Mario’s Stadium to unlock Blue Pianta.

Blue Shy Guy

Shoot the Piranha Plants at Yoshi’s Ballpark to unlock Blue Shy Guy.

Boo

Have DK and Wario solve the block puzzle at Wario City to unlock Boo.

Daisy

Successfully complete Peach’s Stadium to unlock Daisy.

Funky Kong

Save Funky Kong from the Hammer Brother at DK Jungle to unlock Funky Kong.

Goomba

Help Goomba trace his shop at Wario City to unlock Goomba.

Gray Shy Guy

Have Peach get Gray Shy Guy out of the log at Yoshi Park to unlock him.

Green Koopa

Free Green Koopa from the poster at Wario City to unlock Green Koopa.

Green Noki

Unlock and have Blue Noki on your team, then talk to Green Noki at the beach at Mario’s Stadium to unlock Green Noki.

Green Shy Guy

Have Peach get Green Shy Guy out of the log at Yoshi Park to unlock him.

Green Toad

Successfully complete Toadette’s puzzle, then search the bush at Peach’s Stadium to unlock Green Toad.

Green Yoshi

Free Green Yoshi at the manhole at Yoshi’s ballpark to unlock Green Yoshi.

King Boo

Talk to the Tiny Boos in a chest at Wario City to unlock King Boo.

King K. Rool

Defeat all four Kritters at DK Jungle. Then, go to the waterfall, and defeat King K. Rool to unlock King K. Rool.

Kritter

Defeat King K. Rool at DK Jungle to unlock Kritter.

Monty Mole

Use Peach on the Monty outline on the beach at Mario Stadium to unlock Monty Mole.

Paragoomba

Use Yoshi’s ground pound on one of the palm trees in Wario City to unlock Paragoomba.

Paratroopa

Defeat the minion guarding the lighthouse at Wario City to unlock Paratroopa.

Peach

Successfully complete Peach’s Stadium to unlock Peach.

Pink Pianta

Go to Mario Stadium to find Pink Pinata in a palm tree on the beach to unlock Pink Pianta.

Red Noki

Unlock and have Blue Noki and Green Noki on your team, then talk to Red Noki on the giant clam at Mario’s Stadium to unlock Red Noki.

Red Paratroopa

Find the paintbrush at Yoshi Park, then use it to paint the giant billboard at Wario City to unlock Red Paratroopa.

Red Shy Guy

Shoot the Piranha Plants at Yoshi’s Ballpark to unlock Red Shy Guy.

Red Yoshi

Find the brush that Red Yoshi lost, then find him at Yoshi’s Stadium to unlock Red Yoshi.

Tiny Kong

Defeat Bowser Jr. at DK Jungle to unlock Tiny Kong.

Toad

Start Peach’s Stadium to unlock Toad.

Toadette

Talk to Toadette at Peach’s Stadium to unlock her.

Waluigi

Find Waluigi on top of a skyscraper in Wario City to unlock him.

Wiggler

Reset the roller coaster that Wiggler is riding at Yoshi Park to unlock Wiggler. Alternately, win a game at Toy Field.

Yellow Pianta

Go to Mario Stadium to find Yellow Pinata in a barrel and unlock him.

Yellow Yoshi

Use Yoshi to get Yellow Yoshi out of a tree at Yoshi Park to unlock Yellow Yoshi.