Not sure if it be possible in halo 2 but why not make a Ghost act like a paranormal ghost when boosting it can phase through other objects Npcs,Vehichles and some props

As for a sentinel beam weapon you should do two options a rainbow beam which allows for a rainbow sentinel to be apart of the funny roster

another option could be the Numa Numa Yay song machinima the longer you fire the louder the song gets and does more damage

Also amazing to see the mod fully public now was awesome to get to test it before full release

Holy hand grenade?

Miniature Scarab: fires flame beams that ignite targeted enemies (and vehicle moves at half the speed of a Scorpion). Allows 2 NPCs to ride on hull for support.

Rocket Jumper: Fires 0 damage rockets that have massive knockback (and makes the player less likely to die from fall damage).

Stick-and-rock-launching Sentinel Beam

Can you elaborate on the Stick-and-rock-launching sentinel beam?

I think it'd be cool to do something with the grunt funeral skull kinda like in the first cursed halo. When you kill grunts, they could explode into a bunch of rainbow grenades for some good chaos.

I have some oddball ideas to this:
-Wraith boost at Mach speed.
-Cortana doing the Fortnite dance.
-Regret beatboxing (native language) to his followers
-Ghost with no collision to objects and players
-Scarab move in a fast pace at the final mission.
-Jackal speak like a toxic CoD player
-Regret's sick gaming chair.
-Pelican thrusters act like helicopter rotors.

Weapons:
-Homing Sniper Rifle but shoots a slow moving needler round and it hurts like hell.
-Holy Sentinel Beam: Send people to rapture from consecutive hits.

Funny cutscene/in-game scene:
-Cairo Station: Big fart echoes from Athens and Malta.
Jesus Christ flies over the Cairo Station with the Halo theme.
Cortana rapidly fires the MAC cannon and shakes the entire room.
Lord Hood: Permission denied. *Chief do it anyways and Cortana having second thoughts*

-Outskirt: Chief is dead from the crash but wait, you're still here and Johnson is mourning for the whole minute (turns out, you're a brick).
The entire enemy are replace with sniper Jackals, even Jackals with wings!

-The Arbiter: The prophets only offers him a weird suit.
Grunt exploded from methane overload during the phantom cutscene.

The Oracle: The skittles, heretics and sentinels are having a rave party.
Heretic boss isn't real, just a hologram and Arby only grabs the hologram at the end. Tartarus and Guilty Spark have no clue what the Arby is talking about.

-Delta Halo: Suddenly, you stumbled into the dark world with themes and everyone in some sections.

-Regret: Gondola/Elevator moves at an incredibly fast pace (plays the Daytona USA theme).

-Sacred Icon: Marine are getting humped by skittles over the comms.

-Gravemind: Arby and Chief were violently toyed with. Chief is teleported upside down, again.
Everyone at the Mausoleum playing Breaking Benjamin (the music stops abruptly if attacked and everyone starts fighting),

-Gravemind outro/High Charity intro: Mercy is a bit freaky with the flood.

-Uprising : Intro: Arby got teleported to the wrong spot in a cartoon-ish way and correctly teleported back.

Outro: Rtas accidentally fires the wraith at Arby before he reveal himself. Brute aren't good at driving the phantoms (ends up crashing)

-The Great Journey: Human prisoners and Scarab are doing the Caramelldansen dance.

I like a few of your ideas Robert F. I like the teleporting upside down and the weapon ideas.