If the goal would be to kill the Ender Dragon, I could imagine a UHC pack containing the following mods:
Tinker's Construct with Iguana Tweaks,
Hardcore Ender Expansion (duh)
Hardcore Questing Mod with quests eventually giving you an End Portal,
That OpenEnder thing Mikee showed off a while ago
Eternal Isles
And all of those mods in BnB that add the really deadly mobs. I don't play BnB, but I think it's called Lycanytes Mobs or something?