The Skirnir Magus has an ability called "Sorcerous Shield":
At 1st level, skirnirs are proficient with all types of shields, including tower shields, and do not suffer an arcane spell failure chance when casting magus spells while using a shield. They treat their magus levels as their fighter levels for the purpose of qualifying for shield-related feats.
This ability replaces spell combat.
The Throwing part of a Throwing Shield requires Exotic Weapon Proficiency: Shield, Throwing.
Does Sorcerous Shield cover the Exotic Proficiency requirement to avoid a -4 to attacking with a thrown Throwing Shield?
The FAQ doesn't address Throwing Shields and Sorcerous Shield. The class feature doesn't make the distinction between weapon and armor proficiency, it just says "proficient with all types of shields." I was curious to see of there was anything more official, but this seems like it's a question that's 100% up to the DM to answer.
As for throwing my Bonded Object, there's a spell called "Returning Weapon" ;-)
So what is shield proficiency?
Shield Proficiency (Combat)You are trained in how to properly use a shield.
Benefit: When you use a shield (except a tower shield), the shield's armor check penalty only applies to Strength- and Dexterity-based skills.
Normal: When you are using a shield with which you are not proficient, you take the shield's armor check penalty on attack rolls and on all skill checks that involve moving.
Special: Barbarians, bards, clerics, druids, fighters, paladins, and rangers all automatically have Shield Proficiency as a bonus feat. They need not select it.
So all types of shields not all types of weapons.
Shield Bash Attacks: You can bash an opponent with a heavy shield. See "shield, heavy" on Table: Weapons for the damage dealt by a shield bash. Used this way, a heavy shield is a martial bludgeoning weapon. For the purpose of penalties on attack rolls, treat a heavy shield as a one-handed weapon. If you use your shield as a weapon, you lose its AC bonus until your next turn. An enhancement bonus on a shield does not improve the effectiveness of a shield bash made with it, but the shield can be made into a magic weapon in its own right.
Armor proficiencies and weapon proficiencies are different things.
For what you want to work it would have to say weapon proficiency with all shields.
1. Sorcerous Shield doesn't specifically grant the Shield Proficiency feat. Sorcerous Shield says, "At 1st level, skirnirs are proficient with all types of shields, including tower shields..." If it said something along the lines of, "Skrinirs gain the Shield Profiency feat with this feature" or "This counts as the Shield Proficiency feat," then what the Shield Proficiency feat says would be more relevant.
2. I'm asking about Throwing Shields, which is an Exotic Weapon, and the Skirnir Magus archetype. Magi are already martial weapon proficient, so shield bashing was never an issue.
3. The Skirnir archetype is designed to use their shields as weapons, which is why they can Spellstrike with shields at first level.
Again, the class feature doesn't make the distinction between weapon and armor proficiency. It really seems like it can go either way, from a RAW standpoint. I'll just check with my DM.
You need Exotic Weapon Proficiency to use a Throwing Shield for throwing, but not to use it as a normal shield (including for shield bashes). Thus, implicitly like an Aldori Dueling Sword and the Aldori Swordlord Fighter archetype -- this archetype gets the normal Fighter weapon proficiency, which does not include Exotic Weapon Proficiency (Aldori Dueling Sword), so they have to use the Aldori Dueling Sword as a Longsword until they get that feat(*) (fortunately they qualify for it out of the box), since the Aldori Dueling Sword can be used as a Longsword with martial weapon proficiency. Likewise, the Throwing Shield could be used as a normal shield (including Shield Bash) with martial weapon proficiency, but you would need Exotic Weapon Proficiency (Throwing Shield) to be able to throw it without the non-proficiency penalty.
(*)Another example is Bastard Sword: You can use it as a two-handed martial weapon without Exotic Weapon Proficiency, but to use it one-handed you need Exotic Weapon Proficiency (Bastard Sword).