Treasure Island/Scenario Guide
After you have completed your Half-Pipe Coaster, create a spiral staircase on Pool Complex 0's pool deck or use the same platform of Aqua Blaster Slides 1 and create a water slide with an excitement of at least 4.5 with little amount of money as possible. After having some fun drops and curves, since there's almost no way to end a slide from the sides of the pool due to paths (although you could rearrange the paths on the sides of the pool), end the slide in a drop from above. You could use H20slide Bowl's Bowl special element (or just a simple drop without an ending element), but make sure the bowl lands into the pool and make sure it's not too close to the High Diving Platform, otherwise the slide will automatic close down due to the slide being dangerous.
Now the remaining objectives is to have a good park rating (little-to-no litter and satisfying peeps with rides, attractions, and stalls) and to attract more peeps by building more rides since marketing is not available in the scenario. Make sure you set the prices of the rides to match their excitement rate, rounding down, as well as slightly increasing the prices of your shops and stalls to earn enough money as there are no loans to take out, and place an Cash Machine to allow peeps to refill their money.