The card itself makes four 1/1 Hero tokens and then powers up every creature on your board, to reflect the story of summoning your adventuring party and imbuing them with the power of the crystals
Im going to start the format pretty high on this thing though if it ends up being a format that is dominated by aggro, this will drop precipitously
Each deck is built around specific themes, combos, and playstyles, so knowing the structure of your deck will guide your purchasing decisions
"Moon of the Closed Heaven", since "Fiendsmith's Requiem" can be Link Summoned by using any LIGHT Fiend, it is easy for most Decks to access the Fiendsmith engine by using any 2 Effect Monsters to Link Summon "Closed Heaven", then use it to Link Summon "Requiem"
These are also great cards to collect and keep in a binder if you just want to appreciate the great artwork on them