If I have a 4IV Sylveon spread out in 31spA/31spD/31spe/31atk and a 3IV Eevee spread out in 31def/31hp/31spe does it make a difference if I use two Destiny Knots?
No, both pokémon holding a destiny knot when breeding will have the same effect as when only one of them holds a destiny knot.
No, it will have the same effect as using just one.
When breeding you usally want to pass down a Nature to the offspring, and you achieve that giving an Everstone to a parent. If you use two Destiny Knots you can't do that.
I have discovered that giving BOTH parents a Destiny Knot will make them spawn tons of offspring with random natures and zero offspring with just plain stats with a neutral nature. So once you have two 5 perfect-IV parents and you just want to spawn a bunch of perfect 5-IV offspring with random natures until you get the nature you want this is the way to do it. Then, once you get that 5 perfect-IV child with the correct nature you can give it an Everstone and leave the other intended parent of the opposite gender with the Destiny Knot. This is a quicker and more consistent way of getting 5 perfect-IV Pokemon with your intended natures.
But you can get exactly the same effect with one Destiny Knot. The second one doesn't add anything. Jul 16, 2020 at 23:05