What does this feat actually do? it states it makes your shadow 20% stronger but what oes it mean? beter concealment or 20% higher on stealth checks or something else. if someone knows and could tell me i would be thankfull

Shadow spells are illusion spells with the shadow descriptor, like shadow conjuration and shadow evocation. This is not about invisibility or stealth. Shadow spells typically are phantasmal versions of other spells. Like shadow evocation : fireball is just a regular fireball, but cast with illusion school instead of evocation.
The thing is shadow spells have a disbelief check, if you fail the check the enemy knows this isn't the real spell and will get a weaker version of it (or even completely ignore it).
The mythic feat just gives you a bonus to that check (which is usually rolled on a d100, so 20% is pretty much a +20 on that check).

Err... I'm pretty sure the disbelief feature has nothing to do with it either?

When an enemy fails to recognize a shadow spell as one, and instead believes it to be the real deal (whether a fireball or such or summoned creature), it will deal full damage.

Enemies which can see through the ruse will take reduced damage from the evocation spell effect or the summoned creature. The mythic ability makes these shadow effects stronger, increasing their effectiveness against creatures which frequently resist the illusion.

It's a pretty bad ability when considering all the other options.

Originally posted by Drake:

Shadow spells are illusion spells with the shadow descriptor, like shadow conjuration and shadow evocation. This is not about invisibility or stealth. Shadow spells typically are phantasmal versions of other spells. Like shadow evocation : fireball is just a regular fireball, but cast with illusion school instead of evocation.
The thing is shadow spells have a disbelief check, if you fail the check the enemy knows this isn't the real spell and will get a weaker version of it (or even completely ignore it).
The mythic feat just gives you a bonus to that check (which is usually rolled on a d100, so 20% is pretty much a +20 on that check).

so it's more a mythic feat for Nenio then for woljif? thanks for the info so i don't waste a mythic on woljf

It's a waste even on nenio, imho. The ability works only if enemies save against the shadow spell, and your primary concern is for them to not save at all. I would get quite honestly anything other than this. Ascendant element for example.

In tabletop, having a highly varied spell list could potentially be important enough that you'd have sorcerers learn shadow spells, especially if your DM is strict about resting. In Kingmaker/Wrath, where you cast the same few spells over and over again and can rest more or less at will, there's little reason to do so. Especially in Wrath, where as @BlueBangkok says the LAST thing you want to do is give enemies an extra chance to save against your spells.

Originally posted by BlueBangkok:

It's a waste even on nenio, imho. The ability works only if enemies save against the shadow spell, and your primary concern is for them to not save at all. I would get quite honestly anything other than this. Ascendant element for example.

This. Shadow spells would have been helpful because they offer variety in elemental attacks, at the cost of an extra check to save for reduced damage. The plethora of ways you can bypass resistances/immunities makes this feat fairly worthless when measured against a mediocre focused element build.

Originally posted by BlueBangkok:

It's a waste even on nenio, imho. The ability works only if enemies save against the shadow spell, and your primary concern is for them to not save at all. I would get quite honestly anything other than this. Ascendant element for example.

kinda sad then, it sounds in the discription way beter then it actually is :/

Originally posted by art_loots:

Originally posted by BlueBangkok:

It's a waste even on nenio, imho. The ability works only if enemies save against the shadow spell, and your primary concern is for them to not save at all. I would get quite honestly anything other than this. Ascendant element for example.

kinda sad then, it sounds in the discription way beter then it actually is :/

To be fair, the shadow spells themselves are still quite useful, less than in PnP but still good here. The problem is this ability, which honestly doesn't do much.