Tutankoopa will likely start the battle by 
summoning his pet Chomp to assist him. Ignore the
Chomp and focus on killing Tutankoopa. You can't
hit Tutankoopa with your hammer because he is on 
a platform so keep using jump attacks. Tutankoopa
will either throw a shell at you or cast magic
to damage you. The thing is that Tutankoopa
has bad aim with his magic so he'll sometimes
hurt himself with the magic! Just keep attacking
Tutankoopa and he'll fall soon enough. I recommend
using either Parakarry or Goombario to take him 
down. After defeating him you will recieve your
second star spirit: Mamar.