How exactly does Mage Shield work? (in General)

What can it block? I trained spells but it doesn't seem to actually block anything but I remember when I put it on my Mage to test it out it did block his fireball so I'm perplexed now.

The mage shield reduces incoming magic damage on the minion wearing it by 0.75%/+.

"Negates all spells trained by the wearer (except for spells that still function at a zero skill level, such as Decay, Ethereal Chains. e.g. if i equip a MgS on my tank that trains protection it will look like this Protection: 0/8,715 (4) no matter what the level is, it will still have an effect of (4) )"

This is the part I don't understand

All enchantments and DD spells on the minion bearing the MgS will be reduced to level 0. This doesn't necessarily mean 0 effect--EC, for example, has 20 effect at level 0, and the old Protection used to have 4 effect at level 0.

Ok, if you train a Direct Damage spell, an Enchant Offense spell or Enchant Defense spell on the minion that you have MgS equipped on, the MgS nullifies it, reducing its level and effect to zero. The exception being Decay, which still functions if its level is reduced to zero, seeing as Protection was removed from the game.

Did that help at all?

I can say from experience that decay does not in fact function with a mage shield equipped.

Sorry JS you're wrong. Decay does fire with a mage shield equipped. Decay fires at base level and at the same output no matter how much you train. Raising the level increases it's resistance to AMF, but has no effect on it's actual output.

decay works with mage sheild... but the lvl will be 0... even a base AMF would take it down

Oh, right, that's why.... I was going up against AMF.

N/m to all of that. Mage shield does in fact allow decay to fire at full damage, but any AMF will make your decay do 20% damage to yourself.