Build a roller coaster or a whoa belly tower. With the roller coaster, make it a power launch mode and make it fly off the track. Do not test it, just open. With the tower, build it up approximately three times and put it on full speed. Do not test it and people will fly off as they are on it.
Make a shuttle loop roller coaster, have it power launched, with a speed of 60 mph.
Create a large square of road. When guests walk on it, they will become stuck. When nobody is on a smaller square, delete it. When you have one or two of three squares remaining, build water on them to drown all the guests.
To score a fast kill on a guest, click on desired victim, then select the pick up tool (resembles tweezers). Move and drop the guest in water.
Put some water in front of an exit to a ride. All people that get on the ride will drown.
Put water or a pit directly under the exit so people fall straight it and die or get trapped. It is an easy way to keep people in your park.
Dig a large hole and place a large amount of guests in it. Raise the water level to watch a mass drowning of guests.
Build a path that leads to an elevated platform or bridge. The platform or bridge should be several squares all around. Once you have lured a group of guests onto the platform, delete the path(s) that led them there to trap them. Underneath the platform, create a massive body of water (or you can create the large body of water first, then build a platform over it.). Delete the platform and everyone will fall into the water.
Make a water slide. At any point that you can, have a sheer drop, normal drop, sheer drop, and normal drop again. Make sure it is an open track, and not a tube track. After the first drop, it will fly off the track and crash.
Build the shuttle loop roller coaster and change the speed to 60 mph to send the people on the ride soaring through the air and then crashing to the ground.
Build the shuttle loop roller coaster and increase the speed to 60 mph. The coaster will launch off the track.
Research until you get the Steel Coaster or Corkscrew Coaster. Build a station, and then behind it, build a sheer incline with a chain. Put a sheer incline at the other end of the station to make the coaster appear to come back down. Set the mode to reverse-incline and open it. The coaster will go backwards up, and when it gets to the last track it will continue to be pushed by the chain and be forced over the edge of the last track.
To kill guests on any roller coaster, make it go high up, drop down, then up again. When it goes up again, do not build a crank. End the roller coaster. Make it so there are as many trains as possible, but with only one car. When the roller coaster goes down, it will not make it up the hill, and will slam into the next car. It will then explode, killing the guests.