Well, here's a list of cards that are absolutely must haves, and in some cases, you might need to really open your wallet for
You can only use this effect of "Blackwing - Pinaki the Waxing Moon" once per turn
As you might expect, one of the easiest ways to check the value of a card is to look it up on an auction site like eBay
One Adventurous Mouse Arthur, Marigold Knight makes it very easy to get full value out of even the more expensive Adventure creatures by sneaking those creatures directly into play before bouncing them back to hand so you can cast their less expensive spell halves
We have locations in North Carolina, and The Netherlands
Cursed Eldland is the best for that since it searches Eldlich (extender for this specific version of deck) or Golden Land (Huaqero/Conq), it has GY eff to send Eldlich/Golden Land, super good because Golden Land GY eff can set Eldlixir (Scarlet) from deck