It’s time to collect all eight Red Coins on Whomp’s Fortress, which isn’t too difficult to do. Upon beginning the stage, jump up to the dirt path and follow it until you get to the Moving Bars. The middle Moving Bar will have Red Coin #1 hovering above it, so be careful to not get pushed off by the creature. Once you grab the first coin, you have two ways to get to the next one, as you can continue in the same direction or return to the beginning. If you return to the beginning, then you will need to jump up to the stone slope and go to the top of it. There will be a Thwomp (this is the second one if you went the other direction) nearby, so jump on top of it and wait for it to be in the air to see Red Coin #2.
Double back to the stone ramp near the beginning and go into the water. As you get closer to the Bob-Omb Buddy, there is another slope that is too steep to run up it normally. Instead, do a Double or Triple Jump to grab Red Coin #3, then return to the top of the stone ramp once more. Behind the Piranha Plant right in front of you will be Red Coin #4 and around the bend, on the thin ledge will be Red Coin #5. The next Red Coin is in eyesight, but you need to get on the rotating bridge and wait for it to bring you around to it. Once you have Red Coin #6, make your way to the top of the fortress.
Look for the plank of wood that is standing straight up and attack it a few times to knock it over flat. You will now be able to access the floating platforms without having to deal with the janky camera. On these floating platforms will be Red Coin #7 and Red Coin #8. The star will spawn at the base of the fortress, next to one of the flower patches.