There's quite some hidden features in this addon that one might like if finding:

Marines when pressing E on them
Hold and press E on them while holding a ASTW2 weapon they can use, and they'll trade, press walk key + E to have them follow you.

Elite weapon trading
If you write down in chat /IV04SetFaction FACTION_COVENANT or allow the great schism option and then do the same process as with marines about trading, they'll trade weapons.

Ordering marines to hold down an area
Spawn them in defensive mode, press walk key + E on them to have them follow you, do it again to have them stop following you on the place you want them to defend, their AI will hold the position.

Marine morale
One can notice them taunting when they kill quite some enemies, but sergeants can order much more in case of that (order to advance) or the opposite (order to retreat)

Covenant rank logic
Grunt minors flee a lot of the time when an ally dies, while major ranks don't and enter kamikaze instead, aswell that if it was someone of equal rank (grunt minor sees grunt minor dying), it takes more than one to start running around.

Engineer behavior
It doesn't fly around if it is aware of allies, it'll go near them to give them its shield.

Gúta when you are out of reach
It'll start roaring if it can't reach its target.

Aftermath marines
Sgt. Stacker uses his CE voices if the Halo CE NextBots are installed, same thing for Sgt. Johnson.
Marines use their CE versions of voices if the addon is installed.

Weak spots
Hunters can have their back armor blown up to expose their weak true back even more
Grunts can be sent flying if their backpack is shot
Skirmishers, engineers, brutes and jackal snipers gotta lose their helmets first before getting headshot, they can be shot off.

Scarab multitargeting
It's actually possible for the scarab to have two targets at once, if it is attacked by one target while it attacks another and it is within AA gun range.

BOB
1/100 chances that, when spawning an elite ranger, it is the legendary BOB.