As seen in Reepblue's previews for the mod PUNT!

The example map isn't very good, and I'm not actually sure it doesn't leak, but it shows the triggers you need. Copy-paste them into a plain box and it'll look better.

Used with permission, but you need to attribute PUNT to Reepblue if you make something big with this.

File Name: puntcube.7z
File Size: 50.79 KiB
Click here to download PUNT Gravity Cubes

Oops, this is only the gravity cubes. I forgot the freeze and bomb ones. I'll upload them when I finish the example map.