Diamond Heights/Scenario Guide

PC
One of the biggest problems with Diamond Heights is the accessibility to the left unused part of land, after the park entrance. You should build your park expansion there, but it's very difficult to access it other than creating a large bridge from the Shortstuff's Slide ride, and a train stop on the Railroad. The first thing that you should do is focus all Research & Development funds to shops and stalls at first so you can get a Drink Stall. Then, switch it to Thrill Rides and Gentle Rides. This will allow you to build future attractions, such as go-karts and water slides before the end of Year 3. Then build some shops and stalls, as the park lacks them. You should then, and only then, diversify the variety of rides in the park.

While the four roller coasters in Diamond Heights are probably more than enough to satisfy the needs of the guests, you may need to build a fifth roller coaster in order to reach the objective, although this should only be done as a last resort. Shortstuff's Slide may need to be changed to single ride per admission mode, as some guests may ride again and again while complaining about being on the ride too long, and make people in queue wait longer. Even though this will lower the excitement rating, it's an easy choice to do. You can also increase the ride's capacity by allowing 5 riders on it instead of 4.

Make sure you lower the inspection time of both of the dueling roller coasters named Claustrophobia and Agoraphobia to 10 minutes. This is due to the fact that both these roller coasters can crash due to a station brakes failure, which mostly occurs in either the second or third years. Place two mechanics patrolling at the exits of both rides is a very good prevention method for these crashes. An alternative is to reducing both coasters' train count to one and their car count to eight, which will increase the excitement rating yet lower the rides' capacities and therefore benefits. This choice is harder to do than Shortstuff's Slide, but you can do it. Inserting brakes set below 45 km/h (28 mph) or reediting the tracks in order to incorporate a brakes line, might also prove useful.

Once all this is done, the scenario's quite easy to complete : build new rides & rebuild the non-tracked ones from scratch to rebuff the park's value, (try rebuilding the splash or the Agoraphobia if you want a good challenge), build a brand new coaster if you haven't met the requirements at June 31st of year 3, and you should make it.

Android/IOS
Like the PC version, it also has the same issue but the objective is much higher than the original. The only solution to this level is to build more rides or stalls. Build two or four roller coasters along with many gentle rides (it doesn't matter as there's no decrease effect on the same rides). Also, hire more security guards, more cleaners and few mechanics because it will prevent the park rating from dropping twice if vandalism, litter, or broken rides are remained there longer.