Super Mario 3D World (WiiU)

Bonus fireworks
If you touch the flagpole when the last digit of the timer is a 1, 3, or 6, fireworks will go off, giving you 1,000 points each. You'll get one firework when the timer ends in a 1, three when it ends in a 3, and five when it ends in a 6.
Sixth sense
When your player character is near an invisible block, they will look up at it as if it were a normal block. Watch for this hint and you can find lots of hidden goodies.
Unlock Luigi Bros.

You can unlock the bonus Luigi Bros. game by either clearing the castle in World Bowser, or by having New Super Luigi U save data on your Wii U console. On the Super Mario 3D World title screen, tap the Luigi icon in the bottom left corner of the GamePad to launch Luigi Bros.

Luigi Bros. is basically the NES version of Mario Bros. with Mario (player 1) swapped out for another Luigi. The new Luigi wears a green shirt and purple overalls, while the original Luigi (player 2) keeps his white shirt and green overalls. Compared to the Mario Bros. title screen, Luigi Bros. has an updated logo ("Luigi Bros." instead of "Mario Bros."), a green game-select asterisk instead of pink, and an updated copyright date.

Unlock World Star
Clear the castle in World Bowser (the eighth world) to unlock World Star (the ninth world).
Unlock Rosalina
Rosalina will become a playable character after you clear World Star-2.
Unlock World Crown
To open the final world, collect all Green Stars in Worlds 1 through 11, get all gold flags in Worlds 1 through 11, and collect all Stamps in Worlds 1 through 9 (there are no Stamps in Worlds 10 and 11).