How to Make Floating Objects in Forge
From Halopedia, the Halo wiki
The following is how to make make floating objects, bases, etc in the Forge mode of Halo 3.
Floating Base
This is a glitch you can use in Forge to make bases, objects, etc in any map float.
1. Find a map you want to do this in, such as Sandtrap.
2. Take a Radio Antenna or a Crate and stack them to your disired height.
3. Put a Receiving Teleporter(or any other) on top and fip it so you get the flat end up. Delete the towers, crates, etc.
4. Put anything you want on the Teleporter and it will float.
This can be used to makes floating bases, objects, etc in your map. Note- If you make Radio Antenna's more than 5 tall, make sure to put a Sender Teleporter on to at this point and keep building on top of it. It will help the tower not wobble as much.
Falling Fusion Cores
If you want your map to look like it's being bombed, use the method above. When you reach you height, Place a Fusion Core on top then delete the tower. Once the match starts, you will have Fusion Cores falling from the sky. Note- You can also set your respawn time to 10 or 0 seconds.(set run-time minimum and maximum to max setting to do this)