Unit Energy GrassFireWater 170/156

Yes. At $19.23 it costs 44x the set's median card price of $0.44.

Because it is a secret rare. Ultra Prism prints 156 cards in its main run, and this one is numbered 170/156, past the end of it.

Yes, 2 in total. The others are Unit Energy GrassFireWater at $0.49.

No. Ultra Prism printed this collector number once, in one finish, so every copy on sale is the same card.

Buying the single. It is $19.23, below the $51.50 a Ultra Prism booster pack costs, with no chance of pulling something else.

No. The single is $19.23 and a sealed booster box is $1,533, so the card is 80x cheaper than buying a box to chase it.