Bretonnian magic
Bretonnians can take two types of spellcasters, like the Empire: Prophetresses (Lord level) and Damsels (Hero level). However, unlike the Empire, the wizards are not free to choose their lores. Also unlike the Empire, the wizards provide MR: 2 in case of a Prophetress, and MR 1 for a Damsel.
In most Bretonnian armies of approximately 2000 points, you will see one type of wizard: the damsel of the lady. This kick-ass (not really) hero-level character can take two of the best lores (not really); Beasts and Life! Before I explain why these lores are not-so-good for Bretonnia, allow me to expand a bit on how Bretonnian damsels work.
If you've played Bretonnians (and even if you haven't), you might know that Bretonnian knights (ie 90% of the army) can rank up in the "lance formation," a three wide set-up that allows damsels (and prophetresses, for that matter) to be placed in the middle of the unit in order to keep the lady safe. While this obviously has its advantages (like MR, as mentioned above), it also means that the wizard has no line of sight - rendering nearly all spells from the Lore of Life useless. Some spells from the Lore of Beasts are still usefull for Bretonnians - most notably The Wolf Hunts - but generally you have very little to fear from standard Bretonnian armies Magic-wise. Usually, you will see two level 1 scroll caddies, and that's it. Threat rating: 1/10
The game changes a bit when you're facing a Phophetress. She's quite expensive, but has a serious advantage over Damsels: she can pick the lore of Heavens. However, since most other spells cast by the damsels will still be quite harmless (and thus won't drain a lot of Dispell Dice), you should have no problems dispelling the few spells that count, even if you have few Dispell Dice. Lastly, investing in a prophetress means low leadership for the Bretonnian player. You will not see this character often, save for games upwards of 3000 points.Threat rating: 4/10
Lastly, the Bretonnians can take one Wizard as a special character: the Fey Enchantress. Think of her as a Wizard Lord on a War Altar, only the spell from the Altar isn't from the Lore of Ligth but the Lord of Heavens. Ouch, right? This character packs a pretty mean magical punch, especially since she can pick any magical lore and gets +1 Power Dice from her toad familiar. This lady is a force to be reckoned with, and although she has standard weak spellcaster stats, this woman is by no means helpless in combat due to her bodyguards (Grail Knights), Unicorn (+3S on the charge!) and special abilities. However, if your opponent has specifically tailored their Army to take full advantage of the Enchantress' abilities (like allowing 2 units of Grail Knights and having more wizards) the rest of the army will be quite weak, lacking fighting characters. Like with the prophetress, unsupported she will be manageable (but remember the free lore-of-heavens spell!), supported by one or more damsels she still will be mangeable because damsels are pretty much useless. Also, she is a special character, so don't expect to see her too often. Threat rating: 7/10
Lastly, Bretonnian arcane items. Most of them are terrible, with one possible exception: The Silver Mirror. At 40 points, it's a Dispell Scroll that inflicts a S6 hit upon the caster. Fortunately, this is not much of a problem for Empire as you can easily heal wounded characters with your Warrior Priest.
So, that's all! Remember, when facing a standard (2250/2000 pt) Bretonnian army, their magic will be defensive, lacking offensive power except in the rarest of circumstances. When fighting Bretonnia, expect most magic to get blocked if you're targeting knights - peasants are usually fair game. Most Bretonnian armies will feature 2/3 Dispell Scrolls, and with the added MR from the Damsels they can put up quite a big wall. Fortunately, they're not going to hurt you, either.