RE: Forbiden Lore(s)
Beasts? I don't like it. It has its uses, but overall, I just don't like it.
Heavens useful? Heavens will make him wet his pants! Got a hill where he put his ranged battery? Comet! Dragon Princes? Uranon's Thunderbolt! Swordmasters? Forked Lightning! etc.
Against Empire, I'd imagine the Comet to be very useful as well, as they tend to be tightly packed AFAIK. Celestial Shield can also help your unit getting across the table unscathed, and it's a free Banner of Blood Keep.
Tomb Kings will likely be hurt more by Lore of Light. Cleansing Flare with multiple characters on Hellsteeds with 2 Power Stones each will mutilate them (this isn't list tailoring! it works against basically everything... if you try it, please bring a Brep =). But just watch your Elven friend's face when his T3, expensive units are assaulted by D6 S5 hits! You should though, bring a single guy with Lore of Heavens for Uranon's Thunderbolt against Dragon Princes and the general usefulness of that lore.
Then again, you could always use my good ol' creation... The Opera! Give every character 2 Power Stones and Lore of Death, bring two units of Cairn Wraiths with Banshees. Does he have a unit of Dragon Princes? cast D&D! on them until you've got one through. Then focus both units on them. On average (IIRC they're ld 9), they'll take three casualties per Banshee. Keep in mind that this is only on average, which means it can get better, and if you really want to annihilate them, get 2 D&D!'s through on them.
This one is also amusing. First, move the Fell Bats within 6'' of the enemy General's unit. Now cast 2 D&D!'s on it and cast Walking Death on the Fell Bats. Panic, and then you chase it down with the Fell Bats (or a backup-unit of Fell Bats if the first one got charged, etc.).
Then again, DP's might be Immune to Psychology in which case D&D! won't work. But, they hopefully aren't.