Elf-like, fairy-like, ghostly.
OverWorld.
I'm not sure what you mean by secret sprites, but here's a list of all of them and how to get each one: http://www.fogu.com/hm6/chan3/sprites/index.php
If you mean the little red, blue, and yellow sprites they're names are Arthur, Billy, and Carlos
Sprites are graphics that are ripped from video games, mostly from older such. These sprites can be used for comics, animation or games. Sprites usually come in a big sheet of sprites with a background color like green or blue, to make it easy to separate the sprites from the background. Sonic sprites are sprites that are ripped from a Sonic the Hedgehog game. You can see Sonic sprites in action in flash animation on the net, for example in the Super Mario Bros Z series on Newgrounds.com.
Sprites are not real.
Johnny and the Sprites - 2005 Sprites Snow Day was released on: USA: 1 December 2007
Newgrounds Winter sprites: HGVAXUOKZA spooky sprites: Darkghost Wild western sprites: PDRAVCISQJ Food Chain Sprites: oldmanhats
You could always take one sprite from the sheet of sprites.
Sprites - although they aren't technically fairies. Fairies are sprites but not all sprites are fairies.
Newgrounds Winter sprites: HGVAXUOKZA spooky sprites: Darkghost Wild western sprites: PDRAVCISQJ Food Chain Sprites: oldmanhats
Since the Pikmin games do not use sprites, they are none to be found. There may be unofficial custom sprites, though.
Use the Sprites Resource