pokemon mega evolution booster box case Enhanced Sealed – MHDEALSPLUS Secret Powers Awaken Pokemon: Mega Evolution Chaos Rising

That's not particularly helpful or clear, so most players remember that rule as "take out dead cards, bring in answers." In many ways that is true, but it's not the actual point of sideboarding

Hexproof reads this card cant be the target of spells or abilities your opponents control. This means that most of your opponents cards that deal with your problematic cards are null and void

While it is possible according to the MTG rules for a Wall to be created without defender, as of the time of writing (August, 2021) none have been published

The Ledger

If you're ready to build a competitive custom deck, you'll find you need an awful lot of singles that just aren't present in this starter deck