From the Super Mario Wiki, the Mario encyclopedia

Hey guys, this article says that there are eight Dragon Coins but only seven are obtainable in one go; however, this is untrue. You can collect all eight coins at once if you:

  • Start the level as Caped Mario with a Blue Yoshi.
  • Fly up to the area with the four blocks with vines in them, leave Yoshi there and climb up to where the red Koopa Paratroopa is, collecting the Dragon Coins on the way.
  • Stomp the Koopa and bring his shell to Yoshi, then have Yoshi eat it.
  • Fly Yoshi up high and leave him in a safe place where you can get back to him, preferably on the stone near the top below the music blocks.
  • As just Mario, grab the P Switch and throw it over the divider in the middle of the level so it lands on the bottom right hand side.
  • Get back on Yoshi and fall down the right side of the level, collecting the Dragon Coins as you go.
  • When you land, step on the P Switch, then swallow the blue Koopa, and fly up to the pipe.
  • You will be able to get the three remaining coins and finish the level.

Therefore, I am removing the reference to not being able to collect all coins in one go. Thanks! Tiptup Jr. (talk) 17:31, 7 October 2015 (EDT)

Have you tried it? With "Super Mario World (U)" the three coins in the second area do not appear if you got all 5 in the first area. 18:17, 15 January 2017 (EST)