Visit Santa in the Castle

This objective unlocks after you have collected the 5 rings. To complete it just go back to the North Pole and enter the Castle.

Santa

Congratulations! You have foiled Grinchum's foul plan and recovered the Golden Rings!
And by the magic of the rings, Grinchum has been restored back to his true, merry self: Smilegol!
You see, all Flobbits are drawn to the Rings, but somehow, Smilegol was able to snatch them from my castle.
To anyone but me, their allure becomes irresistable the more Rings someone possesses.
That allure eventually tarnishes the holder's Holiday Spirit, which is about giving, not possesing.
That's exactly what happened to Smilegol; that selfishness morphed him into Grinchum.
But thanks to you, Grinchum is no more, and the holiday season is saved!
Ho ho ho, happy holidays!