One item, with every relation it takes part in answered at once: what
drops it and how often, which quests hand it out, which imbuements it is
a material for, and who trades it at what price. The long tails still
have paginated endpoints of their own — /items/{item}/dropped-by,
/rewarded-by, /imbuements, /books, /keys, /sold-by, /bought-by.

used_as_currency_in is the offers this item is the price of rather than
the thing sold, which matters for exactly one item: the gold coin
denominates all but 202 offers in the wiki's data, so /items/gold-coin
answers with the better part of the offers table. Every other item is
ordinary.

The two imbuement keys answer opposite questions and are easy to mistake
for each other. imbuements is the recipes this item is a material
for, so a Green Dragon Leather lists three and a helmet lists none;
applicable_imbuements is what the item can receive, which is the one
an equipment screen wants.