By vanilla method... I made list of tables for what's possible to sync across clients. Which is ...
http://status.halo.dangerzonestudio.com/wiki/Halo-extension%3AHalo_Netcode Sorry, I planned to response this yesterday. I made these research couple years ago, yet it's not fully completed. If someone else has more updated info about what can/can't sync in vanilla, please post here or in some way contact me.
As for scripts, they don't sync at all. However there are workaround with vehicle (not sure about weapon) to be used as a syncing method for scripts. Couple good examples would be rpg_beta6.2 and rpg_beta7 is fantastic example for trigger animation of longsword dropping bomb on covenant ship plus biped switching.
By modded method yet still use non-modded client... For scenery objects, altis94 has a Forge lua script that made it possible for his maps he's working on so far. I'm entirely not sure how it works. Don't have the time to research on this either...
