Nu Wa Build Question

So recently I've been playing Nu Wa and I've been looking up guides and such just to get an idea of how I should be building her, and I noticed almost all of her builds include Obsidian Shard, which gives 33% penetration boost as a passive. However, she has zero penetration to start off with, so technically isn't that boost useless without Spear of the Magus to give her penetration? I could just be missing something, but that's been bugging me.

Obsidian Shard gives you 33% penetration on the enemy's own protections, if I'm not mistaking. Spear of the Magus is better at full stacks, but you can't get it with Nu Wa, unless they walk into her 1

Clay Soldiers.

the thing here is you are reading Obsidian Shard wrong. like prism said it gives you 33% pen on protections.

no god in smite has basic pen without items or an ability. items is the main way of getting pen.

mages only have 2 (3 if we count Void Stone but this is something that's better on tanks)
first option:spear of magus is mostly used on mages with a lot of DoT best example is Anubis as every tick gives a stack (max 3) going into more pen (and anubis has the fastest way to gain stacks is really easy as he has fast ticks on his ult and on his other damage abilities)

the second option is Obsidian Shard which ignores 33% of the protections just as Titan's Bane does. you get this item on mages with a lot of burst or bad DoT abilities (and Nu Wa doesn't have good DoT IMO)

also Nu Wa has some protection reduction if a clay minion hit them when charging

If you want to learn more about penetration mechanic, and how important this stat is, take a look at this
PROTECTIONS AND PENETRATION/REDUCTION