Let me do all that again, but now for six lands instead of four
We could also start building out deck differently to include powerful but situational 1-ofs such as Cavalier of Dawn, Kayas Wrath or Ugin, the Spirit Dragon
Fiery Confluence: I almost put this card into its own section, since it isnt necessarily a sideboard-only card, but it certainly fits the role of utility card exceptionally well
$1.99 Ravenous Slime Commander 2018 $0.35 Accursed Marauder Modern Horizons 3 $0.35 Shock Brigade Tarkir: Dragonstorm $0.49 Aeve, Progenitor Ooze Modern Horizons 2 $0.35 Temperamental Oozewagg Modern Horizons 3 $0.35 Corrosive Ooze Dominaria $0.35 Wither and Bloom Modern Horizons 3 $0.49 Inexorable Blob Shadows Over Innistrad $0.35 Experiment One Gatecrash $0.69 Splitting Slime Conspiracy - Take the Crown $0.49 Oran-Rief Ooze Zendikar Rising $0.35 Colossal Dreadmask Modern Horizons 3 0 results found
You could take the banned Izzet Cutter list from Standard and transfer it into Pioneer and do well, just need to swap out a few basic cards
As a reminder, Llanowar Elves were reintroduced to Standard the last time we had a Dominaria set