Sideboard highlights With the deck itself being a straightforward, finely-tuned machine, the sideboard brings in some variety as well as potential answers
Many, like Wrath of God, are symmetric
That's already better than Dragon's Blood since you can tap this for mana outside of Bubblehead brews in +1/+1 deck matters
The deck in its current form is already extremely stretched in terms of coloured mana heavy on red with three splashes
The aim of this kind of deck is to flood the board with a lot of Skeletons, attack in with all of them, and either deal lethal damage, or keep chipping away at your foes while your own army becomes larger and more dangerous
I like this in any Commander deck with a Commander with a combat damage trigger, like Medomai the Ageless, since you will be including things like Whispersilk Cloak and Rogue's Passage to kill in one hit already