Visit remnantmods.com for more information
http://www.halomods.info/
If you want them to really see everything, have them download your mod.Cascading Server Side changes:
1. Damage
2. Ammo amounts
3. Vehicle/weapon/biped/powerup spawn points
4. Projectiles (More advanced hex modding.)
5. Starting weapons
6. Teleporters
7. Starting health/shield amounts
Non CSS (Joiners cannot see the changes.):
1. Bitmap/shader changes
2. Fog
3. Models
4. Scenery placements
5. Projectile swaps (Without the hex change.)
6. Swaps within the index
7. Physics
8. Added scenery
9. Sky changes
Then, there are a few things out there that are really "semi-css." They are pretty much half experienceable by joiners. In most cases they'll experiance either a lag like sensation, or in the case of projectile swaps that are not css, they'll take the damage that the projectile has, but the joiners wont see the projectile.
Here is a list of these "semi-css" changes that I can think of off the top of my head:
1. Physics
2. Speed
3. Non css projectiles (Damage still works, you just cant see them.)
4. Vehicle swaps within the index
5. Weapon swaps within the index
6. Collision models
7. Unlimited ammo
8. Jumping height