First of all, in order to unlock Hammer Bro, you have to beat Challenge Mode with Bowser. To play as Bowser in Challenge Mode, you have to beat SPECIAL difficulty of Challenge Mode. The credits will roll and pop-up should come up saying that you have unlocked Bowser as a Team Captain. Then do Challenge Mode on any difficulty. Then when you finish, you should be able to play as Hammer Bro.
There is a twist when you play as Bowser.
Since Bowser is the BOSS when you play as the other captains (Mario, Peach, Yoshi, DK and Wario), Lakitu will pop up and say that you set up the Challenge and that you have to wait for the challenger, but you don't. Beat the other teams and return to your castle. Once you arrive, Lakitu will pop up again and say that Mario's team is playing in YOUR stadium! They must have snuck in when you where playing the other teams.
Now you have to go and play Mario's team, but it is not the same as when you first played him. The game lasts for 5 innings on Mushroom, Fire Flower and Star levels, and on Special level it lasts for 7 innings.
This time he will have the other teams' players on his team.
When I played him, he had these players:
Mario, Luigi, Peach, Daisy, Yoshi, Birdo, Wario, Waluigi and Diddy Kong. I don't know why he didn't have DK on his team...
The last item in challenge mode is called superstar. To get it all you have to do is get all the other items on the list. It is 900 coins and only lasts one game. It makes all players better increasing their abilities. I used this item and ended up hitting a homerun with toadsworth!
1 batter- put a fast person who can get on base 2 batter- put a person who can put the ball in play or put another speed person 3 batter- someone who can make great contact with the ball (Mario) and can run the bases 4 batter-power person no doubt about it 5 batter-some one who can put the ball in play 6 batter-your choice 7 batter-your choice 8 batter-your choice 9 batter- the pitcher if he sucks at hitting or the worst player on your team.
1st base-choose a player that is a power person or has good chemistry with the other infielders
2nd base-choose a player that is fast, can throw, and has good chemistry with 1st baseman
Shortstop-choose a player with a decent arm and good chemistry with 1st baseman
3rd base-choose a player that has a very strong arm and has good chemistry with the 1st baseman. You don't need a lot of speed here
Pitcher-it all depends on your strategy. If you want a person with a lot of technique then put him there. If you like fast pitching players then put power players on the mound. If you like players with slow pitches then put speed here.
Catcher-put someone that has a very good arm and has good chemistry with the middle infield
Left field-put a power person for a good arm but low speed of a fast person with no arm
I don't know what people are talking about koopa park but I do know this. It is actually possible to unlock Toy Field in Challenge mode. Here is how you do it. First beat all the minigames with any character on any difficulty. Make sure you don't run out of turns. To go to a minigame press the "a" button on one of the players such as Shy Guy, Pianta, Toad, Magikoopa, and Koopa Troopa. That should earn you about 500 coins and you will need it. Then go to the shop. Go down to the second to last item. It should say seceret map or island map or something like that. Buy the item for 500 coins. Then a pipe will appear right before the bridge going from peaches castle to Bowsers castle, DK stadium or Wario palace. Enter the pipe by pressing up on the analog stick. (The gray one that can move in a circle) or the one you use to move. Then it should lead you to an island just south east of Mario Stadium and southwest of Yoshi Park. You can't set the rules at toy field just as any other baseball game and you have ten turns. The characters are very easy easier then the one in the main menu and I was doing challenge mode on special! Have fun.