Magical Lineage
Benefit: Pick one spell when you choose this trait. When you apply metamagic feats to this spell that add at least 1 level to the spell, treat its actual level as 1 lower for determining the spell's final adjusted level.
Ok, so if a metamagic feat adds one lvl, Magical Lineage will reduce one lvl.
So Shocking Grasp will still be a 1st lvl spell if using Metamagic +1lvl.
But I still don't understand why this is so great. Can anyone explain why this will benefit my magus?
It's not really that great. When it first came out it was excellent because, unlike other metamagic level reduction sources, it didn't prevent you from reducing the level of a spell below it's starting point. For example with Metamagic Master (the best thing for a solo-spell metamagic build ever) or any other level lowering ability and Intensify Spell you could make Intensified Burning Hands a 0 level spell with Magical Lineage, which is pretty awesome.
Unfortunately Magical Lineage got errataed via the FAQ and this no longer works, so it's only useful in conjunction with other abilities that do allow this (like Metamagic Master), which makes it very limited in utility.
Magical Lineage is good for magus for one reason, intensified shocking grasp. Its your bread and butter spell and suddenly it goes from being capped at 5 dice to 10. This is significant damage for a now first level spell.
It minimizes the spell slot change.
Say you cast Extended Aid. Aid is a level 2 spell, and Extended increases the spell level by 1. Now it occupies a level 3 slot.
However, if you have Magical Lineage:Aid, then when you cast Extend (that adds at least 1 level to the spell), Aid counts as a level 1 (1-1) spell, resulting in a final spell slot of 2.
Basically, it means that metamagics that aren't Tenebrous or Merciful (since they have an adjustment of 0) cost 1 less slot level.
