Why isn't my power item passing down the stat I want (Ultra Moon)?

Question

So I'm breeding Crabrawler and I'm planning on passing down a perfect IV in Defense, Sp.D, and Attack.
I've been breeding Pokemon for some years, and have never come across this before.
I got a parent with perfect Attack and Defense, and a Ditto with perfect Sp.D. I had the Crabrawler hold onto a Power Belt to pass down Defense, and the Ditto a Power Band to pass down Sp.D. After a while I noticed something fishy going on with the eggs. Sometimes, the offspring would have an imperfect IV in Sp.D and/or Defense, even though I have the parents holding on to the correct Power Items.

Why is this happening?
I tried to look it up, but could find no explanation.

My only guess is that the Power Items are somehow cancelling each-other out. Can anyone explain this to me?

Either way what I'm doing doesn't seem to be working.
So how do I get an offspring with the desired IV's I want? I can't imagine it'd be Destiny knot, since it randomizes which IV's are inherited...

Answer 1

When both parents are holding Power Items, for each egg, the game will randomly choose one to pass down, and ignore the other. The other stat can still be passed down, but it has the same chance of passing down as if one parent isn't holding a power item.

Source.

Comments

Okay, thanks. I figured that was what was going on. Dang! So, how do I pass down 3 IV's then? Just hope for the best?

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I would recommend using a Destiny Knot. As you might know, normally, only 3 IVs are passed down, so hoping that the game chooses the exact 3 you want is a time-consuming process. But if one of the parents hold a Destiny Knot, 5 IVs are passed instead, which naturally increases the chance of getting the 3 you want. Additionally, it stacks favorably with the Power items; the power item will ensure you get 1 IV, and then the game will still choose 4 others. I believe it can be found in the Battle Tree for some BP.

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Yes, you are right! Thankfully, it's now much easier to get BP thanks to Mantine Surf! You've helped out a lot, thanks for you're answer and thanks for your advice!