Like any market, the world of Pokmon cards has its own rhythm, with prices that ebb and flow
Gravecrawler is also contextually weaker than Bloodghast because there is no Kalastria Highborn/sacrifice outlet with which to abuse it (although Altars Reap is a good start)
5 Brightstone Ritual According to the flavor text, powerful wizards and other spellcasters covet that stone, but Goblins love how shiny it is, and this card is indeed much better for Goblin tribal decks than Wizard decks
"Paladin of Dark Dragon" can Special Summon "Red-Eyes Darkness Metal Dragon" from the Deck, allowing faster swarming of Dragon monsters, and its requisite Ritual Spell Card, "Dark Dragon Ritual", can banish itself from the GY to search a "Red-Eyes" Spell/Trap, such as the "Lord of the Red" Ritual Spell, "Red-Eyes Transmigration"
It's one of the cards we sideboard in the most against midrange and control
In decks that can manipulate the top of the library, Experimental Lab becomes even more powerful