There are a lot of sideboard options available to you, but to run through a few I particularly like, I do think Dive Down gets a lot better in sideboarded games if you know your opponent will be dense on removal for Games 2 and 3, so whilst maindecking this card is unappealing I have enjoyed having access to the card in my 75
Summon: Kujata Summon: Kujata smacks hard and fast thanks to haste and a variety of disruptive chapters
The coolest thing Ive seen New Blood do is steal a Poppet Stitcher to start creating 2/2 decayed vampire tokens
There's probably an argument that Mardu Humans should slot into the number-two slot ahead of Jeskai Cycling (which is highlighted by The Locust God and Niv-Mizzet, the Firemind), but the fact that The Locust God costs about $10 while Alesha, Who Smiles at death is less than $1 after a bunch of reprintings keeps Jeskai Cycling ahead, but just barely
But what about the biggest of them all
Ultra Pro makes some of the best options if you need a long-term sleeve for MTG cards