The sheep idea comes from the Sleepy Sheep move in Paper Mario where the sheep run across screen. Actually, Ewestace is my favorite one I thought of ¬.¬
I figured, like you said, you kind of need a Goomba and Koopa, so that's why the goomba is a spiky goomba. Koopa I figured, ehh, you know that's what they're going to do anyways. TTYD had a bob-omb as the only returning one besides Koopa and Goomba so I figured Boo could be one returning one with the twist of being Daisy. But like somebody mentioned, Dry Bones could be a Koopa swap out. Or maybe even condense and the Clubba could throw his club for a similar feature.
"Do not expect to build up the weak by pulling down the strong." -Calvin Coolidge, 1914
I never really thought of the effect of the Sleepy Sheep as actual creatures. They never show up anywhere but when you use that item. I always just thought of it as a funny animation for an item, and a possible throwback to Mario RPG.
Like how the Fright Mask or Fright Jar (can't remember which, I hardly use either of them) shows an image of Bowser, but I'm sure its not actually Bowser. The sheep aren't actually sheep, just something the item produces.
Todd (Toad): Okay, since I prefer Toads over Goombas anyway, a Toad partner as the tattle man sound okay. Princess Daisy (Boo): No, just no. Mishell (Koopa Troopa): Generic, but okay. Goomby (Spiky Goomba): Sounds like an excuse to add in a Toad AND a Goomba. And the name is bad. Flyle (Fly Guy): A unique perspective on a common ability type. Ewestace (Sheep): No comment. Jeanie Beanie (Bean): Distract enemies? I crush enemies. Scrubba (Clubba): Sounds pretty good, but scraping away dirt is a bit, lame.
If are a JESUS FREAK and are 100% proud put this as your sig. Favorite Video Game Characters: Mario, Sonic, Kirby and Yoshi.