I've played through much of Oblivion in the past, about 4 or 5 years ago. I don't know why I never used the Weakness spells much before. To some extent, I always figured that by the time I cast weakness spells, I could have used that magicka and time to cast direct damage spells, which is partly true. I decided this play through to give them a try, though, just for variety.

Stacking a 100% weakness to magicka, followed by 100% weakness to poison or an elemental damage really makes that following attacks quite a lot more effective, and since even with just 75% Destruction, I can make the debuffs last 12-15 seconds without making the spell too expensive, and having an area attack to boot, means that casting them can make 3 or 4 following spells ALL much more effective. I've also been reading on UESP about the stacking of weakness to magicka plus weakness to elemental, and apparently they multiply together AND the weakness to magicka, (I think?) increases the magnitude of the weakness to element (?), if I understand it correctly:

Original Damange equals X1; New Damage equals X2

X2 = X1 * (Weakness_to_magicka + 1) * ((Weakness_to_magicka + 1) * Weakness_to_element + 1)

Assuming 100% for both weakness spells, I take this to resolve to:

X2 = X1 * (2 * ((2) * 2) = X1 * 8

Is that right? I'm not entirely sure that weakness to magicka increases the weakness to element, but even if it doesn't we're still talking 4 times the damage, maybe 8 times.

In past play throughs, I typically relied a lot on potions to allow me to "mana dump" - fortify intel + fortify luck + fortify magicka + restore magicka means that one strategy is that you *can* just spam out lots of direct damage spells (fire, frost, shock, dmg health).

But, with Weakness spells, I can often just hit a group of enemies with the two debuff spells (with an area of effect), then hit them with one or two fireball or other area element spells and the fight is over, which I can usually do with just a single mana-bar worth of mana, meaning I don't even need potions.

Yeah, weakness spells are great. I've had a couple characters in the past that used them. I've never had one go 100% with anything, but I imagine during later stages of the game this might save a lot of time.

I personally have no idea; I"m terrible with math (especially game math), but someone else surely will have an answer.

Glargg will have the answer. Glargg knows more about Bethesda's games than Bethesda. In fact, when Bethesda wants to remember how they did something in one of their past games they call glargg. If glargg can't come to the phone they say, "Oh, heck, let's just skip it," and leave the feature out rather than risk doing it the wrong way.

And I forgot to mention, another advantage of using Weakness spells is that they will also enhance the damage from enchanted item attacks (like, a staff of firestorm, which might only be 50 damage base, but the weakness spells I think will also enhance their damage as well). Weakness spells make staffs worth using (as staff will often do less base damage than a player-spell, but have the advantage of being rather spam-able).

You're blaming me for the situation, aren't you?

While we're at it, I should confess to some of my other misdeeds, like accidentally knocking down the "Old Man of the Mountain" in New Hampshire, and the BP oil spill. I'm sorry, already!

Jeez, you'd think they'd give a guy another chance. It's not like I meant to break it.

I love those.

I usually use a 80% weakness to fire spell called Tinder Skin.

Once my main character hit 100 in destruction she pretty much destroyed everything with an AoE (10 ft, I think) 25% weakness to fire/frost/shock and a 33-point Fire/Frost/Shock damage spell in only a few hits and still had a decent amount of magicka left over.

It's a pretty potent combination, especially against Altmer (though usually they explode with just the damage spell).