Modifications include:
-Marines hold pistols
-Major elite replace by Ultra elite
-Zealot also replaced with Ultra elite
-Grunt made white in colour
-Jackal made stronger and they always overcharge their PPistols
-Pistols shoot 1.5x more faster and can zoom 8x
-Stealth elites are more aggressive
-I don't know if this is true but the grunts throw grenades in a different way
-Rocket launchers are super-homing
That's all the modifications.
Story: Master Chief went out to the silent cartographer the 2nd time as last time he did, he failed. But alot has changed at his return, the covenant appears to be more aggressive. Grunts are still the same but wear white armor.
His allies were Marine pistoleers and the pistol has an extra function. Jackals are pissed off at how the Chief easily melees and ownz them last time, but this time it will take him several melees to kill them. Their are new elites called
"Ultra" elite, these elites are 5x more powerful than minor elites. Even the stealth elites are pissed off, they shoot faster at the chief. But the good thing is that Bravo-22 dropped in a rocket launcher that can home in! Now the hunters should be no problem.
WARNING: Playing this on legendary is really hard, do it at ur own risk.
Images:
-Marines

-8x zoom

-White grunts

-Ultra elites

Download link: http://www.mediafire.com/file/0tywdwjoiyt/b30.map.zip
BIG UPDATE: First one was too impossible to beat, so i uploaded a new one that the ultra elite holds a sword instead off needler to prevent overkill. Main death cause are because of the needler wielding ultra.
UPDATE: New file updated, filename is not SC mission 2 anymore, but b30.map.zip.
CHANGES IN THIS UPDATE: There are a few invincible ghosts in this map, so if ur bored playing this again and again, why don't u play hide and seek with the ghost? Note: I don't know exactly how many ghosts are there cuz i just found one after days of searching.
Hint: Overshield & Jackal
Happy searching!