Hey, everyone, as you may know, I am a big fan of Mario. So, I bought ..

No there is no problem with marios team. I think he is the best out of all of them. I used him also. It took me a couple tries also but just keep trying. Once you get used to it, it isnt really that hard. The only advice I have is to just keep playing.

Actually, it doesn't matter what captain you choose (I had Mario too), it just matters what team you have. I beat the Bowser Monsters on my first try in Mushroom Level, but then had a 26 game losing streak to the Yoshi Eggs in Flower Level.

It just matters how good you play. It helps to have other captains on your team, because the captains are usually the best overall. I'm not quite sure my exact lineup, but if it helps, I can tell you what players I had when I won, I'll mark the ones I can't remember exactly. I'm not sure if it'll help, but here goes: (with Mario as captain)

My pitcher was Peach.
My catcher was Wario.
My right-fielder was Luigi.
My second baseman was Daisy.

I'm not sure about the following:

Toadette was on my team, although she could have been either left-fielder or first base, although there's more chance she was left-fielder.
Mario might have been my shortstop, but he's my center-fielder now.
Monty Mole might have been my third-baseman.

It helps to play the other teams until you take their captains. After you take their captains, go play Bowser Jr and win so you have the players you missed (or at least some of them), (because you can't play that team anymore). This will help you assemble the best team possible if you haven't done this already.

After you beat Bowser Jr., he will run away, but after you play a game or mini-game he will come back, so if he still has players and you have coins, play a mini-game so he comes back, and then get the remaining players.
If you can them, put in Power players (like DK or Pianta) at catcher (because they are generally slow) or some other position that they are good at and then, when they bat, use charge swings to knock the ball out of the park. Sometimes, if you can do it, put in faster players in the outfield so they can get to balls your slower players couldn't.
Also, if it helps, I usually play with fielding and running on auto, since the computer usually makes the right decision.
If that doesn't work, switch batting to easy.

And if that doesn't work, just keep playing and don't give up, you should win eventually. After all, I didn't give up after losing 26 games in a row.

Ok yeah, I love mario games too so I bought it already but you should probably change like some people so that they match what they are supposed to do like make waluigi pitcher, someone who can solely hit and nothing else for catcher like petee parana and like yoshi at center field dixie at first birdo at second boo for third.

Also try king boo at the right in the field and diddy kong for the left and toad for shortstop (toad actually hits pretty far) and daisy for the other position I don't know what it's called but she can also be a backup pitcher too

Meh, Mario is lame I choose Wario but you can still win.

Use this line-up.
Toad-2nd Base
Peach-Shortstop
Lugi-Pitcher
Mario-1st Base
Island Guy(I forgot his name he should already be on maior's team)-Catcher
Daisy-3rd base
Noki-Right feild
Baby Matio-Left Feild
Yoshi-Center

I guarntee a win.

I would choose Wario's team over Mario's, but it is still possible to win. I recommend trying to get base hits (don't charge up) instead of going for a homer every time. A lot of people who are new to the game will charge up every time. Only charge up Power players or Balance players until you really get a feel for the charge swing. I did this until I got really good at the game. (Now I can hit homers on command almost, even on special cup, it sorta takes the fun out of it! I made the mistake of playing so much I can now recognize the patterns the pitchers use!!)