There's no easy way. Just get a lot of EXP. A good place to get EXP for Mario and Luigi is in the Airway. A good place for Bowser is in and around Peach's Castle. I hope I helped you!
An alternate ending
Here we gooo! (super mario 64) Oh yeah! Mario time! (new super mario bros wii u Wahoo! (various) Thank you so nice! (new super mario bros) Okeydokey! (I remember it from mario vs donkey kong, probably in others too though) I got it! (Leveling up on Mario & Luigi Bowsers Inside Story) Mario number one! Yeah, Mario wins! Wahoo! Oh yeah, I did it! etc (Mario Kart series)
you have to beat the entire game as mario and luigi. get a gold flag on every level as mario or luigi collect all star coins
Well you have to get nine lives. Then in that level die eight times then there wiil be a green box hit and luigi does the level for you
I've heard you can get a different ending if you complete the game at level 17 or lower. I've also you can get ANOTHER ending by finishing the game at level 40 or higher. :)
You have to complete the pumpworks level
An alternate ending
If either Mario or Luigi is under level 17 at the end, chakron will say something different at the end.
way too easy.. just level up the bros and bowser to level 40.
Ok... what you do is fight your wat through the poophead and then you have found your way
Mario and Luigi- excellent!!! badge increases badge power. How do you get it? Reach level 40. Bowser- Intruder Fangs lets bowser attack twice per tun. How do you get it? reach level 40
you got to get the broggy tecnec and you got to be on level 30 and get your hp and sp up lots of it
bowser advances through the cave. arrives at plack beach. fights the sea pipe statue and water spues out
To get the star Rank, you have to get to level 40 with Mario and Luigi. Your reward is the Excellent! Badge. To get the Final Rank for Bowser, you have to get to level 40 with Bowser. Your reward is the Intruder Fangs. They let you take two turns in a row. Hope I helped!
You must have defeated Blizzard Midbus first. Make Bowser breath the cold air from Blizzard Midbus. This will let Mario and Luigi explore the Airway. Hope I helped! P.S. The Airway is the best place to level up fast. :)
After you beat the Stone Blooper, water starts pouring out of it. Bowser starts drinking the water, opening up a new section of his body-- The Pump Works.
The best way is to equip the excellent! (or excellent!! if you are a pro) and the bonus badges (the one with the coin) and fight the monsters in the airway. It is very tedious but eventually you will level up.