As Luigi, go to the left side of the castle, near the waterfall, and you should see a large patch of grass. Crouch, backflip, and hover over to the patch of grass (it's easily done). Now this is where it gets tricky. To your left,looking towards the castle, you should see a slanted hill. Get as close to the edge as you can, and face the castle so your back is towards the hill, slightly slanted towards the castle. Align your camera so that you see the hill and the waterfall. Press "B" and hold it, and press forward. As soon as he lands, release "B" and press "B" again, holding it. Make sure the camera is still facing in the same direction. I cannot stress how important this is. Keep up the process until you finally reach a spot where you should stop sliding, and stand up. Now look towards the top of the tower and jump (long jump to be safe, if you want) towards it. You should now be on top of the castle early, Enjoy your mini-game rabbit.
As Yoshi, it's harder, but possible. On the other side of the fence, there's a small piece of land. Jump on it. Now do a long jump at the waterfall. As soon as Yoshi starts sliding down, press and hold B, and try to get to the big patch of grass near the castle. It may take a few tries. After that, do the same as you do with Luigi.
As Mario and Wario, it's nearly impossible, but you can do it. Go to the right side of the castle and go near the last tree there. Start running on the right side of it. Do a triple jump, and make sure that the second jump lands in the "corner" of hills. After Mario/Wario lands on the hill, wait a half second, hold down R and start bashing A to do a slide kick. If you can do this long enough, you can get to the castle roof. However it's really hard.
Submitted by: Thor; Yoshi, Mario and Wario tricks submitted by Tiigon