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 do 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.
-Flood speaks random commercial lines from Skittles.
-Machine gun turret crosshair spins along with the gunner.

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*
People are occupied inside the hangar station before Chief suck them out to space.

-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 Jackals, even Jackals with wings!

-The Arbiter:
The prophets only offers him a weird suit.
Sandstorm ambient plays a feint Darude Sandstorm
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 random elite at the end as a plot twist.
The hologram can be killed at the start.
Elevator skips the entire fight in a quick flash.

-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 SiIvagunner's Daytona USA theme).
-Chief skeletonize body at the water scene.

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

-Quarantine Zone:
Due to Miranda's continuous spawning of floods, all corpses at the end of the library are reanimated with each different weapon.

-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),
Cortana discovers the entirety of Covenant's search history full of *REDACTED* content.

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

-Uprising :
Intro: Arby got teleported off the cliff 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.

the D20 Grenades may need some the weights looked at, I got like, 15 arbiters.

https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=3621154363

Edit:

Suggestion, make the tiny Rocket Launchers something that can be dual wield. Just makes sense to me!