Do you know that Vacuum move Bowser has after saving that block guy on the stranded island
That move is useful in many ways. I'll list some right now.
 Warning: Spoilers: 

 Toothy: 
-When fighting Toothies at Plack Beach, use the Vacuum move on them. You suck up their
teeth that makes up their bodies and you get a Defense Boost.

 Chuboombas: 
-When you use the Vacuum move on Chuboombas, Bowser will likely suck up the lollipop it is
holding. You instantly win if this happens, because the Goomba will run away. You don't
gain any experience out of this though.

 Chain Chawfuls: 
-Chain Chawfuls can be defeated in a similar way. Do you see that green dude hanging out
of the Chain Chomp That's called a Sworm. You can use the Vacuum Ability to suck out the
Swarm and you'll instantly win the battle, yet you don't get Experience Points.

 Treevils: 
-Treevils that have acorns are stronger than ones without acorns, however Bowser can suck
up the acorn to gain 20HP

 Midbus: 
-When fighting Midbus for the second time during Fawlful's show, the audience will throw
money and food at Midbus if he does a good move. You can use Bowser to use the Vacuum move
to eat these food before Midbus does. Cake, Doughtnuts, and Chicken Legs (whatever you
call them) are some food that are thrown at him and the Chicken Leg gives you an Attack
Boost.

 Coalbits: 
-Coalbits help Choombas in battle. They jump into the Choomba's mouth and it allow the
Choomba to attack more than once for a couple turns. Just use the Vacuum Move again on
them and have Mario & Luigi defeat them
 
~Some other ways it could be used may be to defeat a Boss or capture Blitties.
 Sites: 
-Mariowiki held these pics which belongs to Nintendo